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Student 07 · 12-09-11, 04:56 PM

Hi Piwoslaw,
Great drawing, that describes what I am talking about. I should probably explain the application I am considering. It is winter and I have my crawlspace closed. It would be good to still ventilate it and inexpensively heat the crawl space.
If I understand you correctly, you're saying collect the heat from the stale air before it goes into the HX? I know an ASHP isn't very effective when it is very cold outside, there has to be some heat in the air for it to collect.? I am all for using the HX to save as much heat as possible before it gets vented to outside, but the HX would supply cooled stale air to the HP. I would think that you would want warm stale air going into the heat pump so it can push hot fresh air out.
Some HRVs use an auxillary heating element in the duct that vents fresh air into the home, but it would be better to use an ASHP with a high COP. From my understanding HPs have a higher COP, (produce more heat) when there is lots of heat to be collected. That is why I am thinking that a HE is counterproductive. With a HP the temp on one side depends on the temp of the other side.?
I agree that a smaller heat pump would be better, but between two heat pumps I would choose the one with a higher COP, and I think by supplying warm air to the HP it would achieve a higher COP.
I like your idea of the ground heat exchanger. I did some informal research on an "Earth tube". Most people who use them report mixed results. Some say the moist warm air cools on it's wall and causes condensation in the pipe, which collects dust and eventually mold. I would think you could clean it like a chinmey, so a little maintenance isn't really a problem. One guy I spoke with said it didn't really change the temperature much. He recommended that instead of one large pipe it would have been better if he had used many smaller pipes connected to a manifold. Of course the required lengths and depths of the tubes is a whole other topic.
I will say though that I have considered connecting a HRV to a solar air collector. But like the HP, I think the HE would cool the air coming from the solar collector, and be counterproductive to what I am trying to accomplish. Would it be better to not try to combine all these things?

12-09-11, 04:56 PM	#165
Student 07 Helper EcoRenovator Join Date: Dec 2011 Location: Gresham OR Posts: 35 Thanks: 0 Thanked 3 Times in 3 Posts	Hi Piwoslaw, Great drawing, that describes what I am talking about. I should probably explain the application I am considering. It is winter and I have my crawlspace closed. It would be good to still ventilate it and inexpensively heat the crawl space. If I understand you correctly, you're saying collect the heat from the stale air before it goes into the HX? I know an ASHP isn't very effective when it is very cold outside, there has to be some heat in the air for it to collect.? I am all for using the HX to save as much heat as possible before it gets vented to outside, but the HX would supply cooled stale air to the HP. I would think that you would want warm stale air going into the heat pump so it can push hot fresh air out. Some HRVs use an auxillary heating element in the duct that vents fresh air into the home, but it would be better to use an ASHP with a high COP. From my understanding HPs have a higher COP, (produce more heat) when there is lots of heat to be collected. That is why I am thinking that a HE is counterproductive. With a HP the temp on one side depends on the temp of the other side.? I agree that a smaller heat pump would be better, but between two heat pumps I would choose the one with a higher COP, and I think by supplying warm air to the HP it would achieve a higher COP. I like your idea of the ground heat exchanger. I did some informal research on an "Earth tube". Most people who use them report mixed results. Some say the moist warm air cools on it's wall and causes condensation in the pipe, which collects dust and eventually mold. I would think you could clean it like a chinmey, so a little maintenance isn't really a problem. One guy I spoke with said it didn't really change the temperature much. He recommended that instead of one large pipe it would have been better if he had used many smaller pipes connected to a manifold. Of course the required lengths and depths of the tubes is a whole other topic. I will say though that I have considered connecting a HRV to a solar air collector. But like the HP, I think the HE would cool the air coming from the solar collector, and be counterproductive to what I am trying to accomplish. Would it be better to not try to combine all these things?