Efficiency of compressor assisted HRV

[Lc_shi]

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

[montreal]

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.