Results 1 to 45 of 45

Thread: DX Coil duty

  1. #1
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    DX Coil duty



    hi Guys

    Wondering if you can help me. Im going to have a refurb done on my house and part of it is going to be heat recovery ventilation unit with outdoor heat pump and DX coil in fresh supply ducting to serve the rooms.

    My heat recovery unit will be delivering 340Litres/second of fresh air to a property of roughly 250m2 with ceiling height 2.8m. In summer /25-30C/ I want to cool down to 19-20C.

    Im interested in coil duty /kw/ needed to cool down the house /rough figure/

    Many thanks for ur help

    Peter



  2. #2
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Hi Peter, not as easy as that unfortunatley, cooling the house down is more than just cooling the fresh air (which itself will be partially cooled by your recovery unit.)

    I would call in a local expert (of which there are many on here)

  3. #3
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    well, i had local A/C guy suggesting 12kw on cooling cycle ... which seems a bit low giving size of the house ...i dont know .... just wanted some 2nd opinion
    do you now some A?C expert here on this forum ?

    many thanks

  4. #4
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    I would suggest that you open a new thread, and ask for help/quote in your area.
    If your house is really well insulated, lots of thermal mass, little windows, and enthalpy heat exchanger then 12kw may not be out of the question??

  5. #5
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Peter, as MF stated, flow is far, far to low for 12 kW. Coil will freeze up. You will need +/- double for 12 kW.
    But,.. 360 l/s also seems very high only to refresh your house. You can do it with +/- 150 l/s
    If 12 kW is enough depends on isolation of the house, orientation of walls and especially the windows,..,
    Will your heat recovery unit have an internal summer bypass?
    Do you have garden to pre-cool eventually the fresh air via a submerged tube?

    Just curious, is a balanced ventilation also obligatory in new houses in the UK?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  6. #6
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    hi Pete

    the whole house is very well insulated /air tight/ and no windows are facing north or south

    My main purpose is to really just to refresh the house with fresh air and being able to cool it down in summer to 19 - 20C, thats all

    So if 12kw external duct mounted DX coil is too big for supply of 360L/s of fresh air AND you are saying I would get away with cca 150L/s giving previously mentioned house dimensions - that tells me that my coil duty is WRONG, should be much smaller ?

    many thanks

  7. #7
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Your coil duty is solely determined by the heat load of your house and has nothing to do with the ventilation rate you calculated or wants to install.

    What's well insulated? What's the max heat load of your house (July) taking into account solar radiation through the windows? In Belgium, for new houses, you have to calculate this very precise with software provided by the Government.http://www.energiesparen.be/epb/huidigeversie (only in Dutch :-( )

    Anwsers to the other questions in post 5?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  8. #8
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    Pete

    But obviously flow of 340l/s of outside air is not enough and if I supposed to go down to 150l/s of fresh air supply its even less so the COIL is oversized and must be less than 12kw, no ?

  9. #9
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Or you install the necessary cooling coil -which capacity is unknown for the moment - but estimated on +/- 10 to 12 kW with +/- 600 l/s air flow or you install the max needed ventilation for a proper ventilation of 150 l/s and a matching coil of +/- 3 kW which will not cool enough.

    Or your first flow of 360 l/s and a 5 to 6 kW coil which will serve well 80 to 90% of the year.
    The max load is only for a few days/year.
    Important: ground coil to pre-cool, you will need certainly a summer bypass if you expect excess heat.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  10. #10
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    but my dilema is - if I install ventilation of 150l/s /which supposed to be sufficient/ what do I have to install to cool my whole house in summer ? /as ur saying dx coil of 3kw will not cool enough/ .... so what then ?

    Surely I cant oversize ventilation system by 300% /from 150l to 600l/ ?

  11. #11
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    1st thing is to determine as precise as possible excessive heat in summer to install the cooling system. And increase your desired temperature in summer ...19C is far too cold. Go for 22C as a minimum in summer.

    My daughter will start building her house within some weeks and the excessive heat is 3,0 kW for +/- 220 m.

    You can decrease your cooling system with answers/solutions on my questions in post 5.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  12. #12
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    sorry pete, i know that its probably stupid question - but what is the process of determining excessive heat ?

    my heat recovery is going to have summer bypass, of course and no submerged tube /no idea what that is/

  13. #13
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    We're using software for this.http://apps1.eere.energy.gov/buildin...ad_calculation gives an idea.
    The software we use is the free EPB software but it's in Dutch.
    And also PHPP from Germany to calculate energy neutral houses an passive houses
    Pm me ocne a sketch or a drawing of your house where I can see also the composition of walls and roof and windows.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  14. #14
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Reading between the lines, it seems to me that there is confussion between ventilation and air conditioning.
    You need to know what your AC load is (as Peter 1) as stated, you can meet this load in 2 main ways, circulate the air with in the house (round and round) or 100% fresh air make up (no recommeneded for domestic)
    Also if you are maintaining a constant internal temp why would you have summer by-pass on your heat exchanger. (This is only any good if you have no AC)

  15. #15
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    There have been a lot of posts in the past by people who want to use or have installed the heat pump to heat ALL the air coming in via a fresh air intake and try to satisfy the heat/cooling load. All the comments I have seen were of major disappointments as no one needs that much fresh air to maintain air quality. In Canada the code requirement is 0,5 air change per hour and somewhere I read that the code over there is 7 air changes per day. I don't know how big the house is but unless it is an extremely low energy house, you will be moving huge amounts of cold air (then heated/cooled by the HP) into the house at a very high cost.

    I think it would be better to have a separate "heat recovery ventilator" (HRV as we call them here) which will de-humidify to some extent and in the winter transfers about 70-75% of the exhausted heat to the fresh air.

    The heat pump can then be sized properly for the heating/cooling load. There are ways of combining them but it introduces a lot more design constraints on the house and HP system.

  16. #16
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Quote Originally Posted by mad fridgie View Post
    ...
    Also if you are maintaining a constant internal temp why would you have summer by-pass on your heat exchanger. (This is only any good if you have no AC)
    MF, if you start in the morning with a fresh indoor temperature in a good insulated house, then temperature outside faster increases then inside temperature. If you then don't bypass, you warm up the house with the warmer incoming air.
    If you use the submerged tube for freecooling, then you certainly need one.
    and the vertical version of it

    With these tubes, you can hold the house fresh without any additional AC. There are also some disadvantages
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  17. #17
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    @MikeHolm, that's why I was so surprised about the huge ventilation rate. A house of +/-240 m can be good ventilated with +/- 150 l/s, exhaust in bathroom, toilets and kitchen and supply to all the other remaining spaces where you're living. There are in Belgium strict and controlled rules. If you don't follow those, you don't get your permit to build and if you build it otherwise then stated on the drawing plans, they give you a very high fine.
    From 2020 on and that's not that far anymore, all new houses in Belgium - and I think also in the rest of Europe - must be passive buildings.
    This besides because this has nothing to do with coil duty
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  18. #18
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Maybe I am misunderstanding what you call a heat exchange system.
    My understanding is that it is an Air to Air heatexchanger, or a balanced air system.
    Where the air leaving the house, passes through a heat exchanger to exchange energy with the incoming air (Moisture as well for a ERV)
    are we talking about the same thing

  19. #19
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Sure MF something like this




    and the summer bypass




    or

    Last edited by Peter_1; 17-07-2011 at 09:16 AM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  20. #20
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Quote Originally Posted by Peter_1 View Post
    Sure MF something like this but with a summer bypass in it like this or
    Must be explicit?

  21. #21
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Peter, this is a good manual about ventilation but it's written in German http://www.effiziento.de/fileadmin/D...S_Zubehoer.pdf
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  22. #22
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    I disagree with the air pass when you have air conditioning
    Internal air temp 20C
    Outside temp 30C
    with bypass you introduce 30C air
    without bypass (75% efficient heat exchanger) you introduce 22.5c Air.

  23. #23
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    MF, I edited my post
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  24. #24
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Quote Originally Posted by mad fridgie View Post
    I disagree with the air pass when you have air conditioning
    Internal air temp 20C
    Outside temp 30C
    with bypass you introduce 30C air
    without bypass (75% efficient heat exchanger) you introduce 22.5c Air.
    Agree 100% but it was meant with the ground tube like we install it so many times here in Belgium
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  25. #25
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Due to the passive house standards, AC in houses will be penalized a lot. You will no longer be allowed to install it unless you pay a big fine. A client of us paid 5 /7 months ago 5.500 € because we installed AC in his house (3 indoor units on a multisplit)and it was mentioned on the building plans.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  26. #26
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    The ground tube, is this just an air duct in the ground, lets say at 2 meters, where the ground is at a constant

  27. #27
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Indeed MF, it helps in summer to pre-cool the fresh air and to pre-heat it in winter.





    This picture is a view from the tubes for the new offices of Bayer where no AC will be installed to cool the offices (250 persons) An engineering company (Ingenium) f my city did all the calculations for this.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  28. #28
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Rehau, th main supplier for this system http://export.rehau.com/files/REHAU_..._342100_UK.pdf
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  29. #29
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Thanks Peter, good info

  30. #30
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    We will do it otherwise in my daughters house. While burring the DX coils for the heatpump, we will install in the same trenches also PE tubes.

    These will be connected together, filled with water/glycol and connected via a small pump to an in line coil in the fresh air supply duct of the ventilation system.



    We so avoid germs entering the house via the tube and it is also cheaper to install.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  31. #31
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    hi Pete, brilliant info about that submerged tubes

    however, with all that new ideas and different opinions Im really getting puzzled a bit

    Im pretty decided to use DX coil, heat recovery unit -
    http://www.nuaire.co.uk/catalogue/Co...ery-XBOXER.pdf -house.pdfground - basement.png1st-2nd.png

    and outdoor heat pump .... its just to combine it all together that i dont get ripped off by installers /oversizing, incorrect calculations/
    It was good idea to throw this DX coil topic here otherwise I would never find out that 12kw coil will freeze if just cca 300l going through it - and it was design by profesional

    I just want comfortably to cool my house in summer, to have that fresh chilled air feel inside ....thats all

    Pete, Im sending u some house plans and also briefly explain what I expect to achieve, would be very, very greatful if I could have your profesional input on this

    many many thanks

  32. #32
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    well .... attached 3 files ....didnt go through ??

  33. #33
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    Quote Originally Posted by mad fridgie View Post
    I disagree with the air pass when you have air conditioning
    Internal air temp 20C
    Outside temp 30C
    with bypass you introduce 30C air
    without bypass (75% efficient heat exchanger) you introduce 22.5c Air.
    And you can dehumidify to an extent

  34. #34
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    Peter, I like the underground system but it seems to me that the effect is equivalent to the HRV/ERV in most ways and the HRV/ERV is less expensive. I can see that you can get greater airflow with it but is it needed?

  35. #35
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Mike, as far as I understood the term HRV/ERV correctly, it's not quite the same. You can cool the supply air down to 18C for free in summer when it's 32C outside and preheat it during winter to 8C when it's -5C outside.
    I know houses which are cooled to a stable 22C in summer, even when it's 30C outside without any additional AC.

    And this is becoming the standard in Europe within 9 years!
    I predict that within 9 years the houses will be heated and cooled only by the ventilation system where you will need in our climate +/- 3 to 4 kW to heat the whole house and +/- 3 kW to cool it down.
    I know houses running this way since at least 4 years.
    No radiators nor radiant heating any longer, no gas or oil burner.

    Perhaps 4kWp PV panels on the roof and an electrical heather in the supply air. Very cheap and very reliable and easy to control. And perhaps a small heatpump to heat water in winter (retract waste heat from grey water) and flat panels or vacuum tubes for heating during summer.
    Only this way you can become 100% passive.

    We have to build a heatpump of 4 kW (DX ground coil and radiant water heating) within some months to heat a whole house.
    My daughters future house is >200 m living space and the heatpump will deliver max 7 kW (calculated for 22C indoor in winter and -8C outside)
    A competitor even places the DX condenser as the radiant heater.
    Last edited by Peter_1; 17-07-2011 at 01:01 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  36. #36
    Join Date
    Jul 2011
    Location
    london
    Posts
    9
    Rep Power
    0

    Re: DX Coil duty

    hi Peter

    I have sent you some house plans as you asked, any chance to take a quick glance and let me know what you think ?

    cheers

  37. #37
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    Haven't seen drawings Peter
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  38. #38
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    This week the temps range from 22 at night to 36 in the day with high humidity levels. We have a scale we call the "humidex" (how hot the temp feels with a particular humidity level) and on the thursday it is supposed to be 45-46C.

    I would still need a de-humidifier with the Rehau system. Peter, What systems are used there for de-humidification in conjunction with the Rehau type system?

  39. #39
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Quote Originally Posted by MikeHolm View Post
    This week the temps range from 22 at night to 36 in the day with high humidity levels. We have a scale we call the "humidex" (how hot the temp feels with a particular humidity level) and on the thursday it is supposed to be 45-46C.

    I would still need a de-humidifier with the Rehau system. Peter, What systems are used there for de-humidification in conjunction with the Rehau type system?
    What is your dew point temperature, this could answer your own question.

  40. #40
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    Well, that will vary with location. Are you referring to dew in relation to the buried ground temp, indoor air or surface? The reason i ask is that we seem to have lots of equipment that would be oversized or for use with traditional AC systems but not small capacity units that could be used in conjunction with the rehau tube system (or some other system that cools but may not condense, such as radiant floor cooling).

    With a Humidex of 45C, the actual air temp would be 36 (as an example) and RH would be 75%.

  41. #41
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    Did I lose you Mad, current dew point is 16.7c

  42. #42
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    53
    Posts
    2,556
    Rep Power
    20

    Re: DX Coil duty

    Not lost, just missed the thread!
    If the ground ground temp is below dew point of the ambient entering air then you will get some level of dehumidification.

  43. #43
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    True but I can't assume that especially with a few weeks of 30+ heat so other options should be available. I do know what local commercial options are for de-humidification but Europe tends to be where most new products come from, with the exception of the HRV which was developed here in the 70s.

    I am trying to get a handle on the state of the art.

  44. #44
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    55
    Posts
    5,516
    Rep Power
    27

    Re: DX Coil duty

    We rarely need dehumidification here in Belgium so the problem doesn't arise. I even think it isn't allowed either. You have simple heat recovery units but those used for example by Mitsubishi are enthalpy recovery units, they interchange also moisture and can humidify or dry partially.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  45. #45
    Join Date
    Dec 2010
    Location
    Toronto, Canada
    Age
    54
    Posts
    1,492
    Rep Power
    17

    Re: DX Coil duty

    We have very different weather patterns here. While the temps here are record breaking at 34-40C it is the humidity levels that can approach 85% on a sunny day that causes discomfort and therefor much of our energy goes in removing the moisture. Of course without cooling the temp is really uncomfortable.

    The code requirements here are for HRV's in all new houses and in major whole house renovations and we have been using ERVs (desiccant wheels) for at least 15 years+. Personally I would rather see people open windows once in a while than have mechanical ventilation mandated by code( I don't like the excess energy use). Here you must provide a certain amount of air to each room and exhaust as well. It is not enough to dump bulk air into a house so ducting is necessary.


    here is a video of one product over here
    http://www.venmar.ca/en/video_eng.aspx

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •