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  1. #1
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    Efficiency of compressor assisted HRV



    Hello this is my first post.

    One HVAC product that is used in Europe but rarely found in North America is the heat-pump assisted heat recovery ventilator, such as the Nilan VPL-15.

    So rare are these products where I live that I have had difficulty discussing this subject on local forums.

    I have recently retired and have spent a fair amount of my hobby time trying to bulid a similar HRV by taking a small 5200 BTU window air conditioner and re-boxing it in a way that I can attach four flexible hoses to the new box in order to have access to the inlet and outlet of the evaporator and condensor coils.

    I am operating on a shoestring budget so my AC did not come with accessories like expansion valves, filter/driers, etc. It is a cap tube type.

    I have been operating my creation for a couple of weeks now and I am getting an exchange of air with heat recovery, how much, is hard to measure.

    I am having difficulty determining what percentage of the heat in the outgoing stale air stream is being recovered and reintroduced into the incoming fresh air stream.

    First, let me say that whatever electrical energy goes into driving my compressor and fan motor produces heat that is brought back into my house and I do not consider this heat as part of the equation of rating the efficiency of my HRV.

    I rate the efficiency of my HRV by only comparing the energy extracted from the outgoing stream to the energy added to the incoming stream, independant of the heat from the compressor motor and fan motor.

    Unfortunately, it looks like I am comparing apples and oranges. I find that the temperature of my incoming air stream rises more than the temperature of my outgoing air stream falls.

    Intuitively, the rise in one should match the fall of the other, since energy cannot be created, only transferred. The wildcard in this equation is the role that humidity plays in the relationship between temperature and energy.

    In my system, it appears to take less energy to heat dry air by say 30 degrees compared to the amount of energy that can be extracted when humid air is cooled by the same 30 degrees, and condensation results.

    If my unit is to be exactly 100% efficient, then it would require that the outdoor temperature and humidity be such that after I heat this fresh exterior air and bring its humidity up to the same level as the interior ambiant humidity, then the final temperature of the fresh air would be the same as the temperature of the indoor air.

    Essentially I would be starting with a pound of stale air at a certain temperature and humidity and exchange it for another pound of air from the outdoors restored to the same temperature and humidity, no more, no less.

    For my unit to exceed 100%, I would need to be able to extract more energy from my stale air than I need to process the exterior fresh air back to the starting point.

    The professional Nilan HRV claims to extract a certain number of watts of energy from the stale air stream. What they don't say is how much of that extracted energy is necessary to re-heat the fresh air.

    Thus it is impossible for me to know if the Nilan meets or exceeds 100% recovery.

    I liken the process to riding a bicycle down a hill in hope of coasting all the way up the other side of the valley. In a frictionless world, no pedaling would be required to achieve this. Gravity would do all the work. If one additionally pedaled with the right gearing, one might not only reach the top of the other side of the valley at the same altitude, but have some extra momentum stored up.

    In heat pumps, I wonder if a similar analogy can be made? No matter how cold the temperature is outside, this low temperature makes it that much easier for the compressor to extract more energy from the outgoing air stream. I suppose there are limits to this due to the temperature that ***** will boil at in a perfect vacuum, but this aside, there seems to be the expectation that these devices may well exceed 100% recovery no matter if it is minus 20 degrees outside or plus 10.

    So far, I have not found that my own creation exceeds 100% efficiency.

    I am hoping to hear from any forum member who has some experience with these compressor assisted heat recovery ventilators and knows how well they perform.

    Thanks.
    Last edited by montreal; 02-11-2006 at 03:09 AM.



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    Re: Efficiency of compressor assisted HRV

    heat pump heat recovery ventilator is not same as normal HRV. It includes the dehumidification and supply conditioned air for the required space. The heat recovery is not only in the air side but also in the refrigerant side. Could u give a simple sketch which is better to understand than by lot of words?

    regards
    LC
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    Re: Efficiency of compressor assisted HRV

    I cannot see how you can exchange heat with hoses. I vote for a drawing. Usually, air to air heat exchangers use a heat transfer method such as a revolving wheel or heat pipes. I could not see your method in your introductory question.

    And, as LC says, refrigerant heat recovery methodology is separate and apart from air to air heat exchange.

    I just reread your original question and there are too many questions buried in it. Please simplify your questions to one at a time. You will never recover 100% of the heat.
    Last edited by Dan; 03-11-2006 at 03:58 AM.

  4. #4
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Dan View Post
    I cannot see how you can exchange heat with hoses. I vote for a drawing. Usually, air to air heat exchangers use a heat transfer method such as a revolving wheel or heat pipes. I could not see your method in your introductory question.

    The following link is to a page that has a photo of the professional unit. Half way down the page you see what the interior of this device looks like. What you see is a 5500 BTU heat pump with a reversing valve. There are two independant horizontal chambers with only the ***** plumbing passing through the wall that separates them. The condensor is in the bottom and the evaporator is slightly hidden in the top chamber. There are 4 ports for connecting 6" diameter hoses.

    (Note: because I am too new a member, I cannot post a url. Add the usual "www" stuff before the following text and add ".htm" after it).

    nilan.com/air-exchangers/nilan-air-exchanger-description

    I have taken the same concept but I have used a standard 5200 BTU window air conditioner. I had a sheet metal shop build be a new shell with four holes to attach hoses to.

    Quote Originally Posted by Dan View Post
    And, as LC says, refrigerant heat recovery methodology is separate and apart from air to air heat exchange.

    I just reread your original question and there are too many questions buried in it. Please simplify your questions to one at a time. You will never recover 100% of the heat.
    Here is a second link to the specs of the professional unit. The base model (VPL-15) claims that in winter it consumes 500 watts of electrical energy and returns a grand total 2000 watts of heat.


    (Note: because I am too new a member, I cannot post a url. Add the usual "www" stuff before the following text and add ".htm" after it).

    nilan.com/air-exchangers/nilan-vpl15-vpl25-specs

    First remove the 500 watts from the 2000 watts and you have a net transfer of 1500 watts. The 1500 watts of transfer remains true regardless of the major changes in exterior temperature in winter.

    My question is how much of the 1500 watts is necessary to heat the cold fresh air stream back up to the same temperature as the ambiant indoor temperature assuming we will also be humidifying this same fresh air to the same humidity level as the ambiant indoor air through the use of a separate humidifier?

    Humidification will have the effect of lowering the temperature of this outdoor air heated with our 1500 watts. But inspite of this lowering of temperature, will our final heated and humidified fresh air still be warmer than the stale air we discarded?

    If less than 1500 watts is necessary to achieve this goal, then we have a machine giving us more than 100% recovery. And that would only happen if the stale air we are expelling to the exterior, after passing through this machine ends up being colder (and with less energy) than the outside ambiant air.

    At some point, the weather will be so cold outdoors that even 1500 watts will not be enough heat to bring the exterior air up to room temperature and humidity. In this situation, this machine would be recovering less than 100%. But the average seasonal recovery may indeed exceed 100% in certain climates.

    It has been hard for me to measure the performance of my own creation, mainly because it is difficult to measure air flow precisely and also difficult to factor into the equation the exact extent that humidity (or the lack of it) affects energy measurement.

    My hope in posting here is to hear from someone who has had experience installing a Nilan or its equivalent, and knows how inlet and outlet temperatures vary depending on fan speed and exterior temperature.

    As is the case in North America, it looks like many of you in Europe are just as unfamiliar with this manufacturer.
    Last edited by montreal; 03-11-2006 at 05:37 AM.

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    Re: Efficiency of compressor assisted HRV

    It's surely a good topic. So we try best to keep it going.
    I got the picture for your ref. May it help.

    regards
    LC
    Last edited by Lc_shi; 10-04-2007 at 09:39 AM.
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    Re: Efficiency of compressor assisted HRV

    Hi sir
    I draw a sketch for the futther discussion. The drawing shows the operation in summer and condenser and evaporator can be reversible in winter.
    Pls have a review if it's correct.

    regards
    LC
    Last edited by Lc_shi; 10-04-2007 at 09:39 AM.
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  7. #7
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    It's surely a good topic. So we try best to keep it going.
    I got the picture for your ref. May it help.

    regards
    LC

    Thank you for posting the attachment which shows a picture of the VPL-15.

    I have never seen another company in the world produce a product like this.

    I was running mine today but after one hour, it would begin to frost up and needed 10 minutes for the ice to melt.

    I will be connecting the compressor to my computer and it will automatically start the defrost cycle.

    I have noticed that many things happen when the time approaches when the defrost will be soon be necessary. The compressor amperage drops from 3.5 amps to below 3, the temperature on the suction line drops from 46 degrees F. to below 40, the temperature on the condensor drops from 103 degrees F to below 80, the temperature on the evaporator drops from 38 degrees F to below 30, and a small propeller located after the evaporator stops spinning.

    If I can add a sensor to my computer that will monitor any or all of these 5 conditions, then the defrost cycle would be automatically controlled.

    Or I could do like many heat pumps, use a timer to pause 15 minutes every 35 minutes.
    Attached Images Attached Images
    Last edited by montreal; 06-11-2006 at 03:27 AM.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    Hi sir
    I draw a sketch for the futther discussion. The drawing shows the operation in summer and condenser and evaporator can be reversible in winter.
    Pls have a review if it's correct.

    regards
    LC
    Thank you for taking the time to make a drawing of the VPL-15.

    The fan located in your drawing on the top right side should be moved to the top left side, and the two filters, compressor, and two coils should be shifted to the right side. Then your drawing will be more exact.

    Each coil has its own expansion valve and there is also a reversing valve next to the compressor. There are also 2 detectors for HI-side and Low-side pressure. There is a filter/dryer as well.

    You will also note that the width of the two coils is different and the thichness of the two coils is different.

    I believe that the difference in width and thickness between the two coils is because in summer, we need the condensor (bottom) to be thinner and larger in area than the evaporator (top). In winter, we need the evaporator (bottom) to be thinner and larger in area than the condensor (top).

    In winter, the air flowing across the evaporator (bottom) has little humidity. In summer, the air flowing across the evaporator (top) has much more humidity. In winter, we want to extract as much heat as possible by the evaporator (bottom). In summer, we want to extract as much humidity as possible by the evaporator (top). This explains why there is a difference between the design of two coils.

    If you want to make a drawing of my creation, just imagine a window air conditioner which has the condensor in the back and the evaporator in the front.

    As you can see in my photo, I have replaced the shell with a new metal box with 4 holes to attach flexible hoses.

    There is a fifth hole on the side for maintenance.

    In mine, the air in the house is at 73 degrees F and 35% RH. When this same air exits my machine, it is 38 degrees F and 45% RH. Some water has been removed from this air.

    The outside fresh air is at 40 degrees F and 38% RH, and this air is now heated to 104 degrees F and nearly 0% humidity.

    My compressor and fan draw 460 VA (400 watts) and this energy will heat the air by 12 degrees F when the flow is 110 CFM. So this means that my 104 degree heat air would only be 92 degrees if the 400 watts of electrical energy was not included.

    On my evaporator, I have a reduction of temperature from 73 to 38= 35 degrees F, and a change of humidity of 35% to 45%. This 45% would be much higher if some water was not being extracted by the evaporator.

    On my condensor, I have an increase of temperature from 40 to 92 = 52 degrees F and a change of humidity from 38% to 0%.

    Normally, I would expect the reduction in temperature by the evaporator (35 degrees) to be the same as the increase of temperature by the condensor (55 degrees).

    My 35 degree reduction is probably more because there was energy released by the removal of the water.

    And my 55 degree increase is probably less because to humidify this hot air to the same 35% as the room will lower this temperature.

    So once my machine has replaced a pound of stale interior air with a pound of fresh exterior air heated to 73 degrees F. and humidified to 35% RH, do I have any extra heat left over so that my house furnace works less?

    And how will this efficiency change when it becomes much colder outdoors?

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    Re: Efficiency of compressor assisted HRV

    HI sir
    I made a calculation based on your data-transfer to SI units. Fresh air side heating energy is about 2.0KW and stale air extracted is 1.8kw.
    If the outside temp is colder,the extracted energy from stale air is less and need more electricity power.
    form your data,it seems there's extra heat to your room to reduce your furnace work.

    You can make a detailed calculation to draw up your product. I think the key is the defrost tech,it's a good product. may be you can use electrical heating to defrost and get the gains in the compressor side.

    regards
    LC
    Last edited by Lc_shi; 10-04-2007 at 09:39 AM.
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  10. #10
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    HI sir
    I made a calculation based on your data-transfer to SI units. Fresh air side heating energy is about 2.0KW and stale air extracted is 1.8kw.
    If the outside temp is colder,the extracted energy from stale air is less and need more electricity power.
    form your data,it seems there's extra heat to your room to reduce your furnace work.

    You can make a detailed calculation to draw up your product. I think the key is the defrost tech,it's a good product. may be you can use electrical heating to defrost and get the gains in the compressor side.

    regards
    LC
    Thank you LC for the calculations.

    In your attachment, you show the "fresh air heating-cond (kw)" as 2.01 kw. This should be reduced to 1.6 kw. because the heated fresh air includes 400 watts of heat from the compressor motor. The enthropy of "fresh air supplied" is 41.57 in your chart, and this must be reduced to 35.07 in order to generate 1.6 kw.

    I do not know what temperature the fresh air supplied must be (0% RH) in order to translate to an enthropy of 35.07.

    Can you please give me your formula to translate temperature and relative humidity into enthropy?

    After the correction of these numbers, we will have an extraction of 1.85 kw from the stale air stream and a gain of 1.6 kw in the fresh air stream.

    There is 0.25 kw being extracted which is not re-introduced and this difference may be because my two air streams are not exactly the same CHM. My fresh air stream may be about 10% faster than my stale air stream and this would help explain much of this difference.

    You have listed the humidity in your chart as "g/kg dryair". You show that the stale air stream loses 6.02 - 2.14 = 3.88 g of water /kg of air. With an air flow of 187 CMH, there will be 870 g of water removed from 224 kg of air every hour.

    I calculate that when humidity condenses into 870 g of water per hour, then we get back an energy of 546 watts per hour. Do you agree?

    Also, if we cool 224 kg of air from 22.8 degrees C to 3.3 degrees C each hour, then we remove 1214 watts per hour. Do you agree?

    When I add the 546 watts and the 1214 watts, the sum of 1761 watts and this is very close to your 1850 watts.


    If my exhaust stream is 170 CMH and my fresh air stream is 187 CMH, then I conclude that my HRV machine does not change the way my furnace uses energy.

    I have the benefit of fresh air without having to pay any money to heat it.

    When it gets much colder outdoors, then I will have to spend money to heat some of the fresh air.

    If my machine is to operate more efficiently when the outdoor temperature is colder, then I will need to cool the stale air more than I am doing today. I can do this by slowing down the air streams but I will have to pay more attention to the risk of frost.

    Thank you again for your calculations.

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    Re: Efficiency of compressor assisted HRV

    Hi Montreal
    I'm glad to see the discussion going further. Nilan catalogue is too simple,do you have any detail material about that? I'm not sure if this product better than HRV ventilator + AC system(heat pump/furnace/electrical heating).Hope to have a comparison.

    regards
    LC
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  12. #12
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    Hi Montreal
    I'm glad to see the discussion going further. Nilan catalogue is too simple,do you have any detail material about that? I'm not sure if this product better than HRV ventilator + AC system(heat pump/furnace/electrical heating).Hope to have a comparison.

    regards
    LC

    LC,

    I have no extra material about the Nilan. This product is popular where there is no need for strong heating or cooling.

    In the summer, the Nilan VPL-15 acts like a 5500 BTU air conditioner. It will de-humidify at the same time it replaces stale air with fresh air. The space to be conditioned must be well insulated and small enough for this machine.

    In winter, it can provide 6500 BTU of heat. That may be enough heat if the climate is not too cold.

    The VPL-25 is a larger version that is 2 times as big, and Nilan makes many industrial size machines which are much bigger but use the same technology.

    I have added an attachment which contains my calculations. Please inspect this zip file.

    Thanks
    Attached Files Attached Files

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    Re: Efficiency of compressor assisted HRV

    Hi Montreal
    It's good to discuss on this product. Now I've got a clearer picture of it.
    It's good to use for the environment of higher IQA request. It's better to incorporate with the main AC unit as a fresh air supplier.

    Your name Montreal is same as your location,is it a coincidence?

    Your calculation is very good ,but it should be enthalpy not entropy for air energy change. Only for your ref.

    Hope you share more with us in the future.

    regards
    LC
    I hear...I forget;I see...I remember;I do...I understand

  14. #14
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    Hi Montreal
    It's good to discuss on this product. Now I've got a clearer picture of it.
    It's good to use for the environment of higher IQA request. It's better to incorporate with the main AC unit as a fresh air supplier.

    Your name Montreal is same as your location,is it a coincidence?

    Your calculation is very good ,but it should be enthalpy not entropy for air energy change. Only for your ref.

    Hope you share more with us in the future.

    regards
    LC
    Hi Lc,

    I agree that if you already have a large heat pump system, then perhaps it is possible to mix fresh air into this system without adding an additional HRV appliance. But there will be a temperature too cold in winter to allow the heat pump to operate. The Nilan can operate when it is very cold outside because its evaporator receives warm air from the indoors.

    When it is very cold outdoors, the condensor of the Nilan will receive cold air and the head pressure will drop. But the TXV of the evaporator will adjust to the drop in pressure and the evaporator will continue to absorb as much heat as before.

    In summer, the Nilan will not give much advantage if you have a strong air conditioner which can accept fresh air at the same time as it cools the indoor air.

    My HRV does not have a TXV, so I must find a way to keep the condensor temperature from falling too low in winter. I can lower the air speed of both fresh and stale air streams to maintain the condensor temperature.

    Do you have an idea of the minimum temperature that a condensor must be, so that the capillary tube can still function efficiently?


    Can you please tell me how to calculate "enthalpy" using temperature and humidity?

    Yes, I live near Montreal.

    Thank you again.

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    Re: Efficiency of compressor assisted HRV

    Hi Montreal
    Thanks for your information about nIlan porduct.I think you should keep the condenser temp above 40C which can supply reasonable hot air for room. You're right to think adjust air volume to affect the condenser head pressure.

    enthalpy h=h(dryair)+h(moisture)=0.24t+humidity*(597.3+0.44*t)

    t is air DBT

    It's in SI unit.

    regards
    LC
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  16. #16
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    Hi Montreal
    enthalpy h=h(dryair)+h(moisture)=0.24t+humidity*(597.3+0.44*t)
    I could not get the same result, so I found another formula:

    enthalpy = 1.01t + X[2502 +1.84t]

    where X = humidity ratio (kg water/kg dry air)

    For the humidity ratio, I used your values (divided by 1000).

    Please see the attached table.
    I get the same results as you for the four different enthalpy, except, for the "fresh air supplied" enthalpy, I get 45.54 instead of your 41.57.

    Can you explain this difference?

    Thank you
    Attached Files Attached Files

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    Re: Efficiency of compressor assisted HRV

    I get the same results as you for the four different enthalpy, except, for the "fresh air supplied" enthalpy, I get 45.54 instead of your 41.57.

    Can you explain this difference?
    You're correct. I made a error. Thanks for your carefulness.

    Have a good week!

    regards
    LC
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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    You're correct. I made a error. Thanks for your carefulness.

    Have a good week!

    regards
    LC
    Hi LC,

    I am glad that you have confirmed that I have a good formula to calculate enthalpy.

    Can you please give me the formula to calculate specific humidity (g/kg dry air) using the dry bulb temperature and relative humidity?

    This will allow me to choose the best air flow in the winter.

    Thank you

  19. #19
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    Re: Efficiency of compressor assisted HRV

    Hello to all,

    It has been 3 weeks since I last posted.

    First, I want to publicly thank our forum member Lc_shi for providing me with the mathematical formulas to calculate enthalpy.

    Using these formulas with a rough estimate of the humidity levels in my stale and fresh airstreams, I concluded that my DIY heat recovery ventilator can indeed generate more heat than it consumes, but not by the margin that I had originally hoped for.

    Initially, I had the expectation that (1) the amount of heat that I could extract from the stale airstream was more or less fixed. I based this assumption on the fact that the temperature and humidity level in this stale airstream was quite stable over the season and the capacity of my evaporator coil to remove heat would not vary either.

    I also assumed that (2) the 400 watts required to run my compressor would remain stable as the winter progressed.

    And last, I concluded that (3) as it became colder outdoors, then it would require more energy to heat the cold exterior fresh air to room temperature.

    Assumptions (1) and (2) turned out to be partially incorrect.

    In early November, it was plus 5 degrees C outside, and my compressor was drawing about 3 amps. My fresh air stream was being heated from 4 to 40 degrees C and the heat from the compressor motor was contributing to about 6 of the final 40 degrees. My indoor temperature is 23 degrees C, so there is 40 - 23 -6 = 11 degrees C of benefit.

    My expectation was that if the outdoor temperature was to be 11 degrees lower than the plus 5, then the overall benefit would be zero, that is, my ventilator would be exchanging one kilogram of stale air for one kilogram of fresh air heated to the same temperature.

    Yesterday when the outdoor temperature dropped to minus 5 degrees C., the compressor was drawing 0.29 amps instead of 3 amps. My fresh air stream was being heated to about 32 degrees C. So the compressor was not responsible for 6 degrees of this 32, but more likely only 0.6 degrees. My benefit was more like 32 - 23 - 0.6 = 8.4 degrees C of extra heat, which is more than what I expected based on my assumption number (2).

    Assumption number (1) was also slightly incorrect in that a lower head pressure due to the colder outside air travelling through the condensor resulted in a higher suction applied to the evaporator. This resulted in a little bit more energy being extracted from the stale airstream, assuming that the ***** was being injected at the same rate. With a lower head pressure, this injection rate was probably lower.

    In November, a major problem became frost buildup on the evaporator coil. I put the compressor on a timer and ran it 30 minutes on and 5 minutes off. I found this worked well during the daytime, but at night, frost and ice began to buildup on the evaporator coil. In this case, I would really need a timer that changes its duty cycle with the outdoor temperature.

    My next approach was to place a thermistor at the bottom of the front of the evaporator coil (where the ice was forming) and turn on a defrost cycle depending on the temperature of the thermistor. I found that the temperature of the thermistor in this location did not provide a good indication of the frost buildup elsewhere on the coil, so I re-located the thermistor higher up and pushed it in between two aluminum fins of this coil.

    I found that this worked better, but if a droplet of water arrived on the thermistor, then that triggered a pre-mature defrost cycle. Also when the compressor first started up, there was often a burst of cold from the ***** starting to enter the evaporator coil, and that also re-triggered a pre-mature defrost cycle.

    I also noticed that the air flow at the moment that the thermistor triggered the start of a defrost cycle was variable. In fact, frost was building up on the rear surface of the evaporator coil while the front surface remained dry. Because of this difference, my airflow was often stopping before the front of the coil was cold enough for the thermistor to trigger a defrost cycle.

    The best way to decide when the defrost cycle should start was to monitor air flow and when this flow became slow enough, then that was a sign that the frost buildup was sufficiently large and ready to be defrosted.

    The airflow monitor I built worked well for the last 10 days and gave me defrost cycles of about 20 minutes (compressor off for 5 minutes out of those 20 minutes). Whenever the compressor goes off, the fresh and stale airstreams still continue to flow, but without the benefit of heat recovery. So for every minute that the compressor is off, I have to run the compressor for an equal minute to compensate, before the system can get back to saving money.

    I found that I could reduce my off time from 5 minutes, to 3 and then 2 minutes as the outdoor temperature got colder. A shorter off time means less overall loss.

    In spite of all this, I found today that it had become so cold outside (minus 12 degrees C) that there was too little air flowing through my ventilator to justify its operation, so I shut it off and covered the outside duct openings. The evaporator coil could simply not defrost enough in the 2 minute period to allow a reasonable airflow. If I was to increase the defrost time from 2 minutes back to 5 minutes, then the overall efficiency of the system would drop too much to justify its operation. I conclude that my ventilator works reasonably well as long as the outdoor temperature remains above 0 degrees C.

    Since last summer, I have enjoyed a constant supply of fresh air. I will turn my ventilator back on sometime next March when the outdoor temperature is warmer.

    This leaves me wondering how the professional unit (the Nilan VPL-15) on which I modeled my version, operates in extreme cold.

    The Nilan has a least 4 advantages that my ventilator does not have. (1) It has a TXV which assures that the correct amount of ***** gets sent to the evaporator coil even while the head pressure drastically falls due to a drop in outdoor temperature. Mine does not have this benefit so the amount of heat that my evaporator can extract drops as winter approaches. (2) The Nilan sends all the condensed water to a drain. Mine sends the condensate to the condensor coil to be slung onto that coil, reducing my head pressure when I need it to be higher. (3) The Nilan has a reversing valve which can quickly and efficiently defrost the evaporator coil without losing much overall efficiency. (4) And the Nilan has a courser evaporator coil. My evaporator coil has a very fine mesh which contributes to its 10.7 SEER rating. Having a fine mesh is good in the summer, but in my winter situation, the frost clogs the mesh much faster than if the coil fins were spaced farther apart.

    I will update this thread next year. Thank you for posting your comments.

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    Re: Efficiency of compressor assisted HRV

    Hi montreal
    I'm glad to know your update information about your DIY. It's of value from real case. Hope to see your new post. And I'll have a further review while I have more leisure time.


    regards
    LC
    I hear...I forget;I see...I remember;I do...I understand

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    Re: Efficiency of compressor assisted HRV

    quite an experiment to learn why an air to air source heat pump works poorly as the outside temperature drops

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Lc_shi View Post
    Hi montreal
    I'm glad to know your update information about your DIY. It's of value from real case. Hope to see your new post. And I'll have a further review while I have more leisure time.


    regards
    LC
    Thank you for your good wishes.

    I am no longer operating my ventilator since the outdoor temperature dropped to -10 degrees C last week.

    I miss the fresh air in my house. The temperature is now +3 degrees outside and I am tempted to start the ventilator again. To do this, I must remove one window, about 2 minutes of work.

    I have been monitoring my total heating costs each day to see how much my electrical consumption changes since I stopped using the ventilator. There has not been much change, maybe 3% reduction in my electricity bill when the ventilator is not operating.

    I believe that the secret to having success with this ventilator when it is very cold outside is to dry the stale air before allowing it to enter the evaporator of the ventilator. Having dryer air will reduce the amount of frost that can accumumlate between defrost cycles on the evaporator of the ventilator.

    The best way to dry the air would be to pass it through second evaporator coil which is less powerfull than the first evaporator coil in the ventilator. That would allow humidity to be extracted but without cooling the stale air so cold that the second evaporator coil begins to accumulate frost.

    Also the heat generated by the second compressor could be returned to the house via the fresh air stream.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    quite an experiment to learn why an air to air source heat pump works poorly as the outside temperature drops
    Firstly, I am running my air-to-air heat pump in a different manner.

    In nature, heat flows from a warm location to a cold location, without assistance.

    In a typical air-to-air heat pump, the compressor has to move heat "uphill", that is, it pulls heat from a location which is cold and deposits this same heat at a location which is relatively warmer. Like pumping water up a hill. Air conditioner also work like this in summer.

    In my application, my compressor is pulling heat from a location which is warm, and depositing this same heat at a location which is cold. This heat is being moved "downhill", in fact it should be flowing freely without the assistance of a compressor, as in the case of a heat pipe.

    So when my condensor coil is fed with very cold outdoor air, it become very easy for my compressor to get the ***** gas in this condensor to condense. My compressor is now having less work to do and it can create a greater suction in the evaporator. This greater suction in the evaporator coil causes the evporator coil to operate at a much lower temperature (like a freezer) and that causes a faster buildup of frost in the evaporator coil.

    Having more frost building up in the evaporator coil means that the defrost cycle has to be implimented more often and each defrost cycle imposes a penality on the overall heat recovery efficiency of my ventilator.

    So the problem with my air-to-air heat pump ventilator is that my compressor has too easy a job moving heat from one coil to another.

    If I had zero humidity in my stale air stream, then there would be no frost buildup in my evaporator coil and my ventilator could operate for much longer periods of time without having to stop for a defrost cycle.

    I mentioned in the previous post that the secret might be to use a second compressor and pair of coils to dry the stale air before allowing it to enter my ventilator's evaporator coil where the temperature of the ***** in the tubes might be as low as minus 20 degrees C.

    Thanks for you interest in my experiment.
    Last edited by montreal; 11-12-2006 at 07:31 PM.

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    Re: Efficiency of compressor assisted HRV

    You would be better off with an HRV and an electric duct heater in the winter. Enjoy that cheap power from James Bay and Churchill Falls

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    You would be better off with an HRV and an electric duct heater in the winter. Enjoy that cheap power from James Bay and Churchill Falls
    While our electricity cost about 1/3 of what some European countries pay, our rate has risen to 8 cents a kilowatt hour (tax included) and is no longer the bargain it recently was for heating.

    In fact, on a kilo-joule bases, for many years natural gas was the lowest price fuel. Electricity temporarily gained the number one spot when fossil fuels went up in price in recent years, but gas has recently re-gained the lowest cost fuel in the last year, as the our state owned electric utility has unfrozen their prices.

    Regarding your suggestion of a HRV and an electric duct heater, the typical HRV sold in Canada where it is obligatory in new home construction, uses a honeycomb style core and has an efficiency of 65-85%. These can also frost up in winter and require a defrost cycle. Such defrost cycles usually require the stale warm interior air looping back through the core to melt the frost. The exterior fresh air feed is temporarily shutdown while defrosting occurs.

    Even in winter, the typical 75% heat recovery does not dictate that an in-line duct heater be added in order to raise the final inlet temperature to 20 degrees C. Usually the house's central or distributed heating system will compensate for the shortfall from the HRV which is running at about 100 CFM.

    If you have been following this thread, then you will appreciate that the average HRV in Canada costs about $650 for the device and another $200 for the installation.

    An exception to this is a highly specialize HRV designed in Europe and sold here for nearly 10 times the cost of a honeycomb style HRV.

    This European design uses an air-to-air heat pump and under most conditions is able to extract more heat from the exhaust stream than is required to raise the external fresh air to room temperature.

    The difference between the 75% efficiency the honeycomb versus the estimated 125% efficiency of the air-to-air heat pump results in an operating cost advantage that easily offsets the extremely high initial investment, especially in climates where the average winter temperature is around zero degrees C and the cost of electricity is as found in Europe.

    What my experiment is all about is to see how far I can take a very low cost air-to-air heat exchanger (from a small $100 window air conditioner) and see how closely I can duplicate the performance of the expensive European model.

    It has been difficult for me to measure the efficiency of my creation on a microscopic and macroscopic bases, but I feel that as long as the outdoor temperature is above zero, I have not been that far from 100% efficiency, which is not bad for my investiment being at 1/3 of what an installed honeycomb HRV costs.

    Perhaps next year I will be able to make improvements to allow it to function during my extreme Canadian winters.

    As my device can be re-configured for summer use as a CRV (cold recovery ventilator), it might be of interest to you in warm climates like yours.

    I believe that if you are required to ventilate and cool in your location, then my device will be more efficient than an ordinary air conditioner working along side a pair of push-pull ventilator fans that exchanges stale air for fresh in an otherwise hermetically sealed building.

    Thanks for your comment.

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    Re: Efficiency of compressor assisted HRV

    I am from Northwestern Ontario originally, probably did a few hundred HRV systems with the cross flow heat exchangers as well as some honeycomb ERVs, a lot of them 'Fabrique au Quebec'. Some were made in New Brunswick and had Heat Pipes they were made by EnviroAir and then bought up by the worst manufacturer ever, Brock Engineering Mfg, a POS company, also in Quebec.

    They frost up and go through defrost cycles and operate at temperatures down below -30C, perhaps supplying air at 4 or 5 C that the home heating system will temper indirectly.

    The defrost is typically recirculated room air or an exhaust only strategy. Without a forced air heating system, you may be forced to temper the supply air up to room temperature and a common way of doing this is with a thermolec electric duct heater with an SCR control, also "Fabrique au Quebec". Other wise if you have high ceilings and baseboard radiators, try and supply the air high above a window.

    The HRV system functions under all temperature ranges where as Rube Goldberg devices will be limitied however they teach the experimenter some principles of refrigeration.

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    Re: Efficiency of compressor assisted HRV

    The reason behind winter ventilation is the homes tightened up in Canada over 20 years ago with building codes. Home onwers also weatherstripped homes sealed them up.

    The loss of the drafty homes turns people into their own humidifiers. So while the goal is said to be good IAQ when you ventilate, it is also to keep windows from condensating.

    So there is not much you can do with the moisture but ventilate or use a desicant, if you ventialte and recover energy, you will get frost.

    Hoyme in Alberta sells a passive ventialtor that works off of the furnace fan, but the principal seems wasteful, could be blowing out some pretty warm air.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    They frost up and go through defrost cycles and operate at temperatures down below -30C, perhaps supplying air at 4 or 5 C that the home heating system will temper indirectly.
    Are we talking about a plastic core or a heat pipe in this example?

    If we put aside the amount of energy absorbed and released when there is a change in moisture content in the air stream and look strictly at the dry bulb temperatures, then if our ideal is to get +20 C from the HRV instead of the plus 4 or 5 C that you say is the case, then we are short by about 15 C. The difference between +20C and -30C is 50C and 15C of this represents about 30% loss, so your HRV when working at -30C appears to be 70% efficient.

    One must now examine the penality that a defrost cycle imposes. As you say, there may be a looping back of the stale air or simply running the exhaust alone. If there is a loopback, then the frozen core is going to consume heat that must be replaced later at a different location, and if we are simply shutting down the fresh air stream while leaving the exhaust stream running in order to melt the core, then cold air from the outdoors must be leaking into the house in order to balance out the flow. So our 70% rating may eventually drop to 60% when frequent defrost cycles are called for.

    I agree that if one does not want cool air from their HRV blasing out into a room or hallway, then pre-heating within the duct is a good idea as you say. In my case, I simply introduce this cool air into my central furnace where it gets plenty of opportunity to mix in the plenums so that no register is delivering cool air. But in another home where there are only electric baseboard heaters, sending cool air at +5C into a room would not be welcomed. Most of the time, the air that my ventilator that is blasting into my house is at +30C due to the heat recovery. This is the typical temperature when it is no colder than zero C outside. When my device has to defrost, I stop the compressor for 3 minutes while leaving both blowers running and my blasted air drops to about 7C during those 3 minutes. This is about a much a reduction in efficiency that I am willing to tolerate, else I simply turn it off and live with stale air as I have for the last 14 years before I started this experiment.


    Quote Originally Posted by Abby Normal View Post
    The HRV system functions under all temperature ranges where as Rube Goldberg devices will be limitied however they teach the experimenter some principles of refrigeration.
    My device is definitely a Rube Goldberg type. You should see what the professional european model looks like. It has what mine doesn't - a better designed evaporator coil, a TXV, a filter/dryer, a hi/lo pressure cuttoff switch, a reversing valve for summer use, high quality ball-bearing fans, and an onboard computer. It also costs 35 times what I paid for my window air conditioner having the same 5500 BTU rating.

    Thanks for taking the time to comment.
    Last edited by montreal; 12-12-2006 at 09:25 PM.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    The reason behind winter ventilation is the homes tightened up in Canada over 20 years ago with building codes. Home onwers also weatherstripped homes sealed them up.
    Humidity building up in these sealed homes is as you point out the main reason for the growth of HRV in Canada. Thus they often come wired with humidistats. HRVs were also prescribed in parts of the country where radium gas occurs naturally in the soil below the basement slab.

    Lately, these same HRV are being promoted as essential to achieving the desirable 0.3 ACH ever since indoor fresh air has become a cultural must, if not for any other reason.

    Quote Originally Posted by Abby Normal View Post
    Hoyme in Alberta sells a passive ventialtor that works off of the furnace fan, but the principal seems wasteful, could be blowing out some pretty warm air.
    I did a calculation on what would be the financial impact on my electric furnace bill if I simply had a push/pull pair of ventilators doing 100 CFM continuously. The bill would have risen by $225. So if a commercial HRV can save 70% of this, then we can see how many years it would take to recover the capital cost of a HRV. But what price do you place on benefit of fresh air in the dead of winter?

    Another thing which discourages my experiment is that my home was built in 1979. It has no continous poly vapour barrior, just the kraft paper backing of the fiberglass batts that are stapled as they overlap the studs. On the exterior under the siding are rolls of 4' wide building paper stretched horizontally around the house instead of Tyvec. I am left wondering how much natural infiltration I am getting anyway and to what degree this infiltration compromises my device which is trying to generate a balanced flow of air?

    I once read that some builders connect an exterior duct directly to the cold air return air plenum. The furnace fan causes a pressure buildup within the interior of the house relative to the exterior so that warm interior air is forced into the wall insulation thereby pushing further towards the outside the location where the dew point would otherwise occur within the wall cavity. Having a greater thickness of batt insulation that is warm and dry provides a greater overall benefit, especially when the wind is driving cold air into the wall cavity from the exterior.

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    Re: Efficiency of compressor assisted HRV

    .

    Quote Originally Posted by montreal View Post
    Are we talking about a plastic core or a heat pipe in this example?

    If we put aside the amount of energy absorbed and released when there is a change in moisture content in the air stream and look strictly at the dry bulb temperatures, then if our ideal is to get +20 C from the HRV instead of the plus 4 or 5 C that you say is the case, then we are short by about 15 C. The difference between +20C and -30C is 50C and 15C of this represents about 30% loss, so your HRV when working at -30C appears to be 70% efficient.

    One must now examine the penality that a defrost cycle imposes. As you say, there may be a looping back of the stale air or simply running the exhaust alone. If there is a loopback, then the frozen core is going to consume heat that must be replaced later at a different location, and if we are simply shutting down the fresh air stream while leaving the exhaust stream running in order to melt the core, then cold air from the outdoors must be leaking into the house in order to balance out the flow. So our 70% rating may eventually drop to 60% when frequent defrost cycles are called for.

    I agree that if one does not want cool air from their HRV blasing out into a room or hallway, then pre-heating within the duct is a good idea as you say. In my case, I simply introduce this cool air into my central furnace where it gets plenty of opportunity to mix in the plenums so that no register is delivering cool air. But in another home where there are only electric baseboard heaters, sending cool air at +5C into a room would not be welcomed. Most of the time, the air that my ventilator that is blasting into my house is at +30C due to the heat recovery. This is the typical temperature when it is no colder than zero C outside. When my device has to defrost, I stop the compressor for 3 minutes while leaving both blowers running and my blasted air drops to about 7C during those 3 minutes. This is about a much a reduction in efficiency that I am willing to tolerate, else I simply turn it off and live with stale air as I have for the last 14 years before I started this experiment.




    My device is definitely a Rube Goldberg type. You should see what the professional european model looks like. It has what mine doesn't - a better designed evaporator coil, a TXV, a filter/dryer, a hi/lo pressure cuttoff switch, a reversing valve for summer use, high quality ball-bearing fans, and an onboard computer. It also costs 35 times what I paid for my window air conditioner having the same 5500 BTU rating.

    Thanks for taking the time to comment.
    The units with the cross flow HX's frosted up, they were typically plastic or aluminum

    They are the most efficient when the temperature differential is minimal.

    They would be doing quite well if they could reclaim 70% during extreme cold.

    They defrost by many methods, straight exhaust, recirculation of room air, recirculation of mechanical room air.

    If you increase the setting on the duct heater it will provide you with some 30C air as well.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by montreal View Post
    Humidity building up in these sealed homes is as you point out the main reason for the growth of HRV in Canada. Thus they often come wired with humidistats. HRVs were also prescribed in parts of the country where radium gas occurs naturally in the soil below the basement slab.

    Lately, these same HRV are being promoted as essential to achieving the desirable 0.3 ACH ever since indoor fresh air has become a cultural must, if not for any other reason.



    I did a calculation on what would be the financial impact on my electric furnace bill if I simply had a push/pull pair of ventilators doing 100 CFM continuously. The bill would have risen by $225. So if a commercial HRV can save 70% of this, then we can see how many years it would take to recover the capital cost of a HRV. But what price do you place on benefit of fresh air in the dead of winter?

    Another thing which discourages my experiment is that my home was built in 1979. It has no continous poly vapour barrior, just the kraft paper backing of the fiberglass batts that are stapled as they overlap the studs. On the exterior under the siding are rolls of 4' wide building paper stretched horizontally around the house instead of Tyvec. I am left wondering how much natural infiltration I am getting anyway and to what degree this infiltration compromises my device which is trying to generate a balanced flow of air?

    I once read that some builders connect an exterior duct directly to the cold air return air plenum. The furnace fan causes a pressure buildup within the interior of the house relative to the exterior so that warm interior air is forced into the wall insulation thereby pushing further towards the outside the location where the dew point would otherwise occur within the wall cavity. Having a greater thickness of batt insulation that is warm and dry provides a greater overall benefit, especially when the wind is driving cold air into the wall cavity from the exterior.

    I have seen them installed for radon gas.

    Ideally in a cold climate you want a nuetral pressure ventialtion scheme or one that is slightly negative with out causing combustion problems.


    Homes from the 70s were time bombs, in particular those with atmospheric gas fired appliances. They were sealing up the homes by weather stripping, expanded foam, new windows and on the verge of backdrafting.

    Humidifier use declined.

    When these homes upgraded to induced draft furnaces, suddenly there was condensation problems when none existed before. The 24/7 ventialtion of an atmospherically vented furnace with a 6 inch flue and a draft hood (and therefore dilution air) was lost.

    A drafty house is a dry house and if it is necessary to run a humidifier a lot in the winter, then most likely you have a high natural infiltration rate and would not really need the mechanical ventilation.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    .
    If you increase the setting on the duct heater it will provide you with some 30C air as well.
    I can get 30C with only using 400 watts to run my machine when it's 0C outside.

    If your HRV is 70% when it's zero C outside, then you would get back about 14C without a duct heater and to get the other 16C, you would need about 950 watts of extra heating, if the flow is 100CFM.

    But mine can't operate below 0C, whereas yours can.

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    Re: Efficiency of compressor assisted HRV

    Lol, for half the year, the average temperature in NW Ontario is at or below 0C.

    And it is still recovering heat.

    Above freezing the HRVs are pretty efficient.

    You live in the wrong country Rube

    Consider migrating.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    A drafty house is a dry house and if it is necessary to run a humidifier a lot in the winter, then most likely you have a high natural infiltration rate and would not really need the mechanical ventilation.
    Suppose my home is that drafty, then that means that my drafts are costing me money because I have to heat all that air which leaks in.

    If so, I agree, I don't need to amplify the ventilation mechanically. I should then reconfigure my device to work like an ordinary air-to-air heat pump with the evaporator being fed outdoor air.

    My device will still try to absorb as much heat as it can when the outdoor temperature is about zero C. The compressor will have to work a lot harder because it will be pumping heat from a cool area to a warm one, rather than the other way around as is my current configuration. Because the outside cold air is dryer in winter than my interior warm air, my evaporator might not frost up as fast as it does right now. So my COP will be much lower, but fewer defrost cycles might help compensate.

    Of course, my 5200 BTU heat pump is not going to generate a lot of heat, but what little it gives might offset the cost of heating the cold air that leaks into my house right now.

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    Re: Efficiency of compressor assisted HRV

    so you are back to an air source heat pump and noticed you they really fall off when the temperature source drops below 0C.

    Perfect for spring and fall. Tits on a bull in the dead of winter.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    Lol, for half the year, the average temperature in NW Ontario is at or below 0C.

    You live in the wrong country Rube

    Consider migrating.
    Here in southern Quebec, we can get nearly 9 months of above freezing weather. I'm not trying to invent anything that works in Siberia.

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    Re: Efficiency of compressor assisted HRV

    search "Bin Weather" some times, see how Montreal tallies up, Compared to Europe or the USA, you are Siberia

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    so you are back to an air source heat pump and noticed you they really fall off when the temperature source drops below 0C.

    Perfect for spring and fall. Tits on a bull in the dead of winter.
    Like most air-to-air heat pumps, the COP drops off too much when you get well below freezing. Mine will be no exception.

    Still, if it will pump 5200 BTU when the outdoor temperature is moderate, that's not bad for a $300 piece of hardware.

    I'm going to bed now. Speak to you another time.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by montreal View Post
    Here in southern Quebec, we can get nearly 9 months of above freezing weather. I'm not trying to invent anything that works in Siberia.
    155 days with temperatures at or below freezing

    http://www.theweathernetwork.com/wea...9.htm?CAQC0363

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    155 days with temperatures at or below freezing
    <http://www.theweathernetwork.com/weather/stats/pages/C02019.htm?CAQC0363>
    Look at the following link and search for Montreal and go to the bottom list of links and select monthly data for 2005.

    http://www.climate.weatheroffice.ec....hlydata_e.html

    You will see that the MAX MEAN TEMP is above 0C on 9 months out of 12 and on the months where it is below zero, it is not by all that much.


    Of course, the MEAN TEMP is colder for all months than the MAX MEAN TEMP, but my point was to show that if zero C is the point at which my device begins to work less efficiently, there are many, many days in winter here in Montreal where my device could run efficiently during the warmest time of the day, long enough to refresh the stale air in the house in order to get to the next day.

    If we navigate over to the 2005 monthly data for Timmins Ontario, we see that there were 4 months where the MAX MEAN TEMP was below zero C, and each of these months was by a larger margin than the 3 months in Montreal that were below zero.

    So I think you will agree that it is definitely colder in Timmins than Montreal, and a HRV like mine which barely squeaks through in Montreal would be snowed under in Timmons.
    Last edited by montreal; 13-12-2006 at 06:30 PM.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    Ideally in a cold climate you want a neutral pressure ventiltion scheme or one that is slightly negative with out causing combustion problems.
    I have heard that anytime you create a negative pressure within a house, you run the risk that fuel burning appliances might be backdrafted, or toxic fumes from a car running in an attached garage might get sucked into the house.

    I recall this claim when someone warned against installing powerful ventilators in attic crawl spaces to exhaust the builtup heat captured by roof shingles in Summer and transferred through the roof deck into the interior attic space.

    So apart from this caviat, why do you think it would be beneficial to have the interior of your house at a slightly lower pressure than the outdoors?

    Would that not lead to sucking exterior air into the house via all the microscopic fissures in the building envelope?

    Any mold in the wall or ceiling cavity would be sucked in at the same time. Would it not be better to create a slight positive pressure within the house and blow all the contaminates outdoors?

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    Re: Efficiency of compressor assisted HRV

    Stack effect infitration is negative pressure. A slight negative is different than installing a 600 CFM range hood

    If it is slightly negative it means that outdoor air, which is the dry air in the winter time, will pass through the building envelope. This air will not contact a surface at/below its dewpoint.

    When a ventialtion scheme creates a slight negative or positive pressure, there is no natural infiltration under normal conditions. How you set the pressure controls how air moves, either in or out.
    Last edited by Abby Normal; 13-12-2006 at 05:46 PM.

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    Re: Efficiency of compressor assisted HRV

    bin weather does it by the hour, have fun with your device in the spring and fall.

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    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    Stack effect infitration is negative pressure. A slight negative is different than installing a 600 CFM range hood

    If it is slightly negative it means that outdoor air, which is the dry air in the winter time, will pass through the building envelope. This air will not contact a surface at/below its dewpoint.

    When a ventialtion scheme creates a slight negative or positive pressure, there is no natural infiltration under normal conditions. How you set the pressure controls how air moves, either in or out.
    Two last questions if you don't mind.

    Can I conclude that if my home is naturally leaky, then if I run my HRV, it will alter the natural leakage that was previously occurring, either by increasing it in some rooms or reducing it in others, depending on which way the wind is blowing and how unbalanced my (heat recovery) ventilator is?

    As one can measure the amount of leakage in a house using one of those instruments they temporarily install in the door frame, would there be a threshold of leakage, above which, no practical benefit in energy savings can be derived from a HRV?

    Thanks for your comments and I'll pick up the project next spring.

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    Re: Efficiency of compressor assisted HRV

    If the HRV exhaust the same amount of air as it supplies, it would be a neutral pressure scheme.

    In NW Ontario, I would guestimate that around 0.7 natural air changes per hour or higher, that you probably had to run a humidifier.

    So you could get a blower door test, or you could ask your self, do I run my humidifier in the dead of winter or not?

    A drafty house is a dry house.

  46. #46
    montreal's Avatar
    montreal Guest

    Re: Efficiency of compressor assisted HRV

    Quote Originally Posted by Abby Normal View Post
    A drafty house is a dry house.
    But is a dry house necessarily a drafty house?

    Could a house with a good exterior air barrier but with an antiquated interior vapor barrier, be a house which has a low air infiltration rate but a high permeability rate?

    I have always wondered if my house could be such a case.

    I know that in summer if I leave the windows shut without the ventilator running, an odor from the carpetting builds up quickly.


    In winter, I usually get water and frost building up on the inside of my windows in spite of it being quite dry inside (RH under 30%). But that is primarily because the exterior pane in my double pane window is held in place with plastic clips and there are a few gaps that let fresh air get into the space between both panes.

  47. #47
    stuartsjg's Avatar
    stuartsjg Guest

    Re: Efficiency of compressor assisted HRV

    Hi,

    Ive been doing something allong the same lines but for space heating as opposed to ventillation.

    Please see this thread.

    forums/showthread.php?t=9280


    Thanks,
    Stuart

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