hi sirs
Is there practical product of dual source heat pump (e.g. air and ground source)?
It could be used in cold area.
Welcome any input
regards
LC
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hi sirs
Is there practical product of dual source heat pump (e.g. air and ground source)?
It could be used in cold area.
Welcome any input
regards
LC
Why would you want air source if you have already ground source? Ground source will work all year round and no defrost but it will be more expensive.
Hi :) LcQuote:
Originally Posted by Lc_shi
some high end heat pumps us this, with a small ground loop to produce heat whilst the air heat exchanger is defrosting.
The air source is more efficent air at 12 deg c will give more heat than water at 10 deg c.
Kind Regards. Andy:)
hi Andy
Agree with you. But it's not widely used, I think:)
thanks
regards
LC
hi while your on the subkect of heat pumps, we are in attempting to sort a problem with a ground source heat pump, well a few actually) where they ave no capacity control and when heating the water tank only they are tripping on hp. i would welcome your comments on how to either apply an inverter or some other form of capacity control you may think applicable.
Well, it will not trip on HP unless the controller ignores the water temperature and/or is required to heat the water up indefinitely. As long as warm water temp is controlled and monitored, I don't see why it should trip on HP.Quote:
Originally Posted by davej
And no, an air to water heat pump at 12°C ambient is not more efficient than a ground source heat pump with water at 10°C. Also, it will take much more space and will be more expensive.
to futher explain the reason why water is more efficient than air is simply in the fact that water has a cv of 4,2 kJ/kg and air 1kJ/kg!
What is the boilertemperature set at? if it's above 45dgrC it will tripp at hp because this is ussually set at 50 to 55 dgrC!
I've worked on a few in Holland with pretty good results! (After changing all the piping from and to the well, because most advisors take to little pressuredrop over the well!)
what is happening they are trying to get 55c water temp, and of coarse the units trips. the system is using a plate heat exchanger and does fine until the water temp get close to the set point the heat pump head pressure just keeps rising to the trip point.
As long as service pressure of PED vessels is 29 bars, that is corresponding to a very high temperature and with the help of the appropriate compressors and R407c or R134a, you will be able to get 55°C water temperature with no problem.
Vapour injection compressors from copeland are able to deliver water up to 62°C. Ultimately, if everything else fails, replace the hp pressure switch with one having a higher cutout.
Sure is with R410a you are not going very far, and you have to drop your arms.
Hi nonickname, thanks for your comments, am interested about the copeland compressor, is that a scroll compressor ? (we are using scroll at the minute).
we could just up the hp trip point but due to the return water temp being so close to the set point there is little to temp dif to condense and the discharge keeps rising. hence the need to find suitable capacity control or off loading via valves.
davej, what you say doesn't make sense. You could potentially increase the condensing pressure as much as safety valve is concerned.
There's no need of capacity control for your application.
Yes, the vapour injection compressor is a scroll
nonickname, youre correct to say we could increase the settings but we are then operating at the top end of the compressor operating range(so we are informed by compressor suppliers)and we concern for the long term operation of the compressor, and pressure continues to rise to 500psig which isnt really a good idea. dont you agree
500 psi is 34 bars which is no good, I agree.
Replace R410a with R407c or R134a and you will be able to get much higher temperatures.
If you replace the ***** all you'll do is decrease the pressure's, not the temperatures the unit operates on! If you want to get over 55drgr of water you'll need abouth 60 to 70 degrees of gas and won't be able to condens it far enough to maintain a useable liquid for the txv since near setpoint the entering water will be apr. 55 dgr and thus the exiting *****!!!!!!!!!!
We have units running on a watertemperature of 75°C while condensing at 18 bar (261 psi) for R22.
I think some forget the higher discharge temperatures.
I'm not saying it isn't possible, but what is the inlet watertemperature on these units? 55dgr of water at inlet will never give say 20 to 30 degrees of liquid!
http://www.refrigeration-engineer.co...ghlight=boiler
Inlet is 70°C and more ;)
Forgot some pictures
The 2nd picture is the inclinde loading platform in concrete, snow melted by the heat of the compressors.
Installed +/- 15 years ago.
Notice the pack we made with unequeal compressors in a mathematical row, no oil separators, no oil floats, still the original machines in place (Prestcold, now Emerson/Copeland),
The snow melting is done by flexible PE pipes burried on the wire mesh in the concrete.
the problem will not accour in the systems u use, ok! But Davej was talking about a plate heat exchanger! Unless i''m wrong these systems tap water from the bottom of the boiler and add it at about 3/4. The water will reach setpoint throughout the tank with these systems when no water is extracted.
I've worked on some heatpumps using a plate heatexchanger and all of these will work till 45dgr.
I've seen similar setups like yours used with great succes! But unfortunally some people are not willing to think about it and go for the bucks!
A former employer of mine installed heatpumps from viessman which uses two plate heatexchangers to cool down water from a well from 10 to 4 degrees and heat water from a boiler and the floor heating to 45 degrees. Increasing the setpoint to 50 would trip the HP because they use std copeland compressors with R22 or R407c.
The water from the boiler was heated to 63dgr using an electric heater! Never could get him to install a similar system to yours! but then again he made more mistakes like this! (like removing freecooling on a system using water from the Amstel in Amsterdam!):confused:
Quote:
Originally Posted by Peter_1
Hi Guys:)
You can get about 25 to 30% of you condenser THR at high grade heat, 5k below discharge temperature without raising the head pressure and 80 to 100% at 3k below condensing temperature. So for 43 deg c water you need to condense at 46 deg c, OK for space heating but useless for hot water for washing.
This basically what we do is use the condenser as a subcooler whilst heat recovery is on.www.thermosavesystem.com
Kind Regards Andy:)
P.S link is for information not advertisement as we have more work than we can handle on our heat recovery side.
And for the faint hearted I am not in the photos as I had wandered off with a drink in my hand
Kind Regards Andy:)
I still don't understand the point. I will try to design it myself.
Go for a compressor having an envelope of 60°C max and R407c (at that temperature it will condense below 28 bar, rule of thumb I don't have a ruler here now). No HP trip.
Condensing at 60°C will release water leaving the condenser at 53-54°C.
Now take the very same water and return it to a desuperheater, with hot gas entering 80°C.
Now the water is 60° or better. Still no HP trip, besides be careful of a low pressure trip (extracting to much heat from high side without controlling it is a bad idea!!).
Be careful in selecting the appropriate pumps and delta T across the two PHE.
Second design: leave the condenser alone and just use a desuperheater (like Peter suggested). You will be able to extract just a 20% of heat, but at a higher temperature than 60°C.
Essentially the idea of Andy in other words.
http://www.3e.uct.ac.za/downloads/re...superheater%22
This is a good one.
hi, i am new. thank you for all your knowhow, i am building a small dual source system. it is a split type variable output rated at 7kW. the thing will run almost continuously which concerns me regarding depth of the well. it will have little rebound time.-how deep? mont
the reason for the air source is to reduce ground heat dmand and cop rises on the air source in the shoulder months-needs some decent programming on variable ballance points-this 7kW system is for retrofit old homes on small lots- i am open to any help
thanks for all your informations. i am looking forward to more discussion on this subject. because this is promising area.
best regards
yangchenchen
Hi The problem you have with the HP tripping may be caused by your coil/heat exchnger in your cylinder reducing the flow from the heat pump this will not allow enough heat exchange across the plate heat exchanger causing the high pressure.Quote:
Originally Posted by davej
Hi. I am investigating a dual source heat pump.air, and some ground source. installed a direct exchange unit last month and noticed in a/c hot gas line going into ground at 160F. seems if pre cooled, loop field could be smaller and less costly. same with heating, liquid line going into ground at about 15F, could be pre heated with ambient air.
15°F for heating seems very cold for a DX system. This must be more something like 40°F with the temperatures we had the last months. Seems your DX loop isn't that big at all :eek:
You could indeed pre-cool it with air but have you taken in account the additional (lost) power you will use then to run the fan?
You preheat now also the soil for the coming winter.
In heating mode, as long as the outside temperature is higher than the soil (+/- 52°F) , then you don't benefit from an additional aircoil.
You indeed don't need in cooling mode fewer coils in the ground then you need while in heating mode. But the coil must be sized to meet the biggest demand for you whole system seen over a year which will be heating when it's freezing outside where you will need then the largest coil.
So, you anyhow need this large DX coil which seems too small in your case. And the bigger it is in summer, the better and lower your machine will condense in summer, the larger the COP will become.
Improving with an air-coil will only be valid for some days during the year.
PS You better started a new thread for this.:off topic:
I thought this was a thread on dual source heat pumps. anyway, the largest manuf. of direct exchange in u.s. now sells an auxiliary fan kit to help with the very hot summer.