Heatpump HRV.

[randen]

The quest for efficiency goes on. Our home in Canada sports a HRV however two problems prevailed. While the HRV is operating in extremely cold winter weather the incoming cold air is unable to be warmed by the outgoing exhaust air with the result of cooling the home. The second problem was the fan motor stopped as a result of a dry bearing. (easy fix and why the hell would a company use a cheap oil-lite bearing and not a sealed ball bearing????)

During winter I would disable the HRV. The utility room containing the HRV would get so cold.

Here is a opportunity for improvement. A little thought lead me to think that huge improvements can be made with active heat transfer. A small compressor and two heat exchange coils would move the heat to the desired air stream.

A small compressor from a dehumidifier and a moderate airflow through the HX coils should do the trick.

Another thought, would the system benefit more from omitting the exhaust airs HX and use the heat energy from my Geo-thermal ground loop via a brazed plate HX.

What do you fellows think.??

Randen

Can someone open and paste the drawing??

[stevehull]

randen, keep talking. This may get interesting. How much energy to move these btus ?


Steve

[randen]

Steve

I was thinking a very small compressor 500 watts. It's probably just a dream but say having the exhaust air from the home exit at close to 0 Deg.C. to prevent the evaporator from turning to an ice ball. And the incoming fresh air 20 + Deg.C. to help warm the house. And the reverse in the summer months.

As I write this it occurs to me I'm asking for a 100% recovery of the air exchange. Maybe the compressors rejected heat would get me close???

The heat-pump HRV is just a small air to air heat-pump.

When the HVR was operational I had its control with a smart home system. It would operate at certain times and occupation of the bathrooms kicked it into high. No sense in having the thing run when we are off to work and the home empty.

It is very impressive the air quality. I would notice the house had a very fresh air smell entering the home. The kitchen freshness recovery after cooking a big meal was another huge bonus.

Looking to a return of the HVR only on my terms!!

Randen

[AC_Hacker]

Originally Posted by randen

The quest for efficiency goes on.

A small compressor from a dehumidifier and a moderate airflow through the HX coils should do the trick.

What do you fellows think.??

I think the idea is quite sound.

Using a dehumidifier is a great choice. You already have all the parts you need, and they just require a bit of re-arranging.

Dehumidifiers operate by chilling air until frost forms on the evaporator, then they go into a de-icing cycle (which is the removed humidity), then they begin again.

Some of the very small units just use a pause in the running of the compressor, and the ice melts. This might be aided by the close proximity of components, and a natural 'reverse flow' occurs... I'm guessing a bit here.

Some of them, larger units, use a reversing valve that reroutes hot refrigerant to the evaporator coil to melt the frost.

I'd recommend starting with a very small unit, remove the cover, let it run and observe how it operates.

I actually did this and it was very instructive. I measured the time between cycles of run-melt-run and found the time periods to be similar but not equal. This made me realize that the 'thingie with wires' that was attached to but not actually touching the lower part of the fins. It was in the area close to (but not exactly at) the place where the the refrigerant was spraying into the HX. It was a sensor of some kind, most likely a thermistor. It appeared that when the frost advanced to reach the sensor, the freezing temperature was the trigger to begin the defrost cycle.

So all the components are there. The two HXs will need to be separated so that outside air goes through the condenser coil, and inside air goes through the evaporator coil.

It might even be possible to gently separate the coils without rupturing the connecting tubes. It would be worth the try, but if they break, you have total power to reconfigure to your exact needs, and you know where to get the refrigerant.

* * *

I suppose someone with astounding cleverness could re-purpose the existing circuitry. Otherwise...

Sad to say it, my friend... You will probably need to lose your Arduino virginity at this point.

https://www.youtube.com/watch?v=OQOLTHK9Hvs

Best,

-AC_Hacker

[AC_Hacker]

delete please

[DEnd]

Originally Posted by randen

Another thought, would the system benefit more from omitting the exhaust airs HX and use the heat energy from my Geo-thermal ground loop via a brazed plate HX.

What do you fellows think.??

Randen

Can someone open and paste the drawing??

Your existing heat exchange core is the best bang for the buck you can get. It uses fan power you would be using anyway to effectively move the heat. You basically only have 23ºC of energy to harvest out of the out going indoor air. A heat pump is not going to do this any more efficiently than your HRV core. What you really need to do is add energy to the incoming air after it leaves the HRV. A heat pump pulling energy from outside the house is a great way to do this.

[AC_Hacker]

DEnd,

You might be right, but how did you come up with:

Originally Posted by DEnd

Your existing heat exchange core is the best bang for the buck you can get.

How do you know that to be true?

Originally Posted by DEnd

You basically only have 23ºC of energy to harvest out of the out going indoor air.

How did you come up with this? Heat pumps are able to scavenge energy when simple, passive heat exchange lack the delta-T to function effectively.

Originally Posted by DEnd

A heat pump is not going to do this any more efficiently than your HRV core.

How do you know that to be true? Do you have real examples or better yet, math that would indicate that this is the case?

Originally Posted by DEnd

What you really need to do is add energy to the incoming air after it leaves the HRV. A heat pump pulling energy from outside the house is a great way to do this.

You are probably thinking air-to-air heat pumps, which will not be very efficient where randen lives. As I write randon's location will be 17 F this evening.

However, he does have access to GSHP heat which would be useful, In your suggestion.

-AC

[jeff5may]

23 degC is a pretty good gradient for transferring heat across. Much of the heat transfer across that gradient will be the latent wringing of humidity from exhausting indoor air as well. A phase change system would definitely leverage the effectiveness of the HRV, especially due to the relatively low airflow through the unit. Like a fridge, dehumidifier rigs are designed to run with at least a partially frozen evaporator and survive a long time. During defrost mode, the evaporator would still be effective at doing work, although the condenser wouldn't be adding heat back indoors.

[randen]

It may be wishful thinking but to have the exhaust air leave the HRV at -5 Deg.C. and the incoming air heated to 30 Deg.C. to augment the space heating.

I ve started my search for items.

Randen

[Steve Tjiang]

Great Idea, but the Europeans are way ahead of us on HRVs.

Nilan, a Danish company makes a commerically available residential HRV that uses both passive heat exchange and active heat exchange. You might get some ideas from there. Search for "Nilanuk combi 300" on Google to get the english spec for the device. I can't post links since this is my first post.

The Nilan box may not be certified for North American use but I think this company has imported some. The company is called airxsolution.com in Quebec

The company also offers minotaur, an active heat exchanger based HRV.