Solar air warmer for ASHP

Piwoslaw · 08-28-11, 01:37 PM

What if an ASHP was to draw air from a solar hot air collector? Has anyone tried this?

As long as there is no air flow restriction then the slightly higher air temp would raise the HP's COP, while at worst it would be the same as with no collector.

The collector could also have a bit of thermal mass, which would store some heat if the sun is shining while the HP is off.

iamgeo · 08-28-11, 01:56 PM

Pardon my ignorance, what is ASHP, HP and COP?

Piwoslaw · 08-28-11, 03:19 PM

Quote:

Originally Posted by iamgeo

Pardon my ignorance, what is ASHP, HP and COP?

Sorry about that:
HP - Heat pump
ASHP - Air source heat pump
COP - Coefficient of performance, ie how much more (heat) energy you get from a heat pump than you put in (to run the compressor).

Heat pump - Wikipedia

iamgeo · 08-28-11, 03:27 PM

Thank you. Now I understand your question.

strider3700 · 08-28-11, 09:21 PM

you'd think the ASHP would "use up" the heated air from the collector quite quickly so you'd get minimal gain. Of course if your collector is massive then it's a different story. It's probably far easier to just feed the heated air into the building though. This way you can be gaining heat anytime the sun is shining not just when the sun is shining and the heat pump is running. Even on the coldest days mine doesn't run constantly. maybe 50% of the time

AC_Hacker · 08-28-11, 10:29 PM

Quote:

Originally Posted by Piwoslaw

What if an ASHP was to draw air from a solar hot air collector? Has anyone tried this?

There's a house here in Portland called the Rose House that uses this kind of scheme.

It not only boosts the efficiency of the ASHP, it also reduces the temperature of the PV array and boosts it's efficiency, too.

See this link.

-AC_Hacker

solarman · 10-12-11, 09:25 PM

Hi, new to this so pardon my blunders.

I've been toying with this idea for years, but never put anything together. Way I see it, solar heating panels give pretty good heat during peak sun, but we loose a lot earlier in the day or later in the afternoon. Also light clouds will put the output of a system to zero real quick. Adding an ASHP will do unbelieveable things, I think.

During peak, shut down the HP, let the high gain of the panels do all the work. When the sun is low in the sky and the output is lower, turn on the HP using a closed loop system. Now the temperature of surface of the flat plate (or cans, downspout, whatever) will drop due to the colder return air. This raises the efficiency of the collector tremendously because the heat lost back to the atmosphere through the glazing is much less and the heat output jumps back up.

Next benefit, the temperature of the air or water out of the HP will be higher than it is even in peak sun conditions, although there will most likely be less volume. This higher temperature will give you a higher gradient for pushing that last little bit of heat into the thermal mass you are using to store the heat.

Sizing might be tricky, but I figure it all comes down to heat content. A 4'X9' flat panel in New England will recieve about 2900 Wattshours of energy from the sun at peak conditions. At 70% efficiency (number may be high but I've read claims of 80%) you get 2000 WattsHours, or just about 6,800 BTU per hour. At less than peak, an old 5000 BTU AC window unit would have the capacity to boost the efficiency of the system. Don't know a lot about refrigeration, but I suspect the design operating temperatures/pressures of an old 5000 BTU window system are quite different than what this setup would give us, so it would probably need modification of some sort.

If anyone has built such a system and can comment, please do. I haven't found much written about such a combo system.

menaus2 · 12-01-11, 12:12 PM

I have a gas water heater that will need replacing soon, and I'm considering replacing it with a ASHP model. I also have a hot air solar panel that I could use (and prevent from self destructing or wasting the heat) during the summer months. Would running the 40 watt blower for the panel negate any efficiency gains given to the heat pump on the water heater? The panel is approx 3x16 ft. screen type with single layer polycarb glazing.

Student 07 · 12-25-11, 05:25 PM

Hi,
I have been doing a lot of reading about air source heat pumps lately, I have had the same idea, and so here is what I found out.

Air source heat pump (ASHP) water heaters have to be installed in a warm area like a basement. They suck warm air out of the basement and blow cold air out into the basement. They usually require a large room, more than 1000cubic feet.

In my opinion they are kind of self-defeating, and the basement has to be heated to counteract the cold air from the HP. I think you are paying for the heat with this system.

An ASHP pool heater gave some great information. They can be installed in an enclosed area that is heated, but the cold exhaust air should be vented to the outside to stay efficient. If the exhaust is vented out then makeup air has to be brought in. I don't know how many CFM an ASHP moves but I am sure it is a lot. The incoming air would have to be heated very quickly or have a very large source of warm air.

If an ASHP water heater requires 1000 cubic feet of warm air: a 3 ton ASHP would need something significantly larger, like a large solar green house filled with warm air. Every time the ASHP turns on it would exhaust the warm air in the green house and refill it with fresh cold air which would have to be heated some before the heat pump turns on again.

If you had a 10'x10'x10' solar greenhouse, it would contain 1000ft^3 of warm air. If the ASHP moved 350cfm, it would empty the greenhouse of its heat in ~3 minutes.

Basically I am saying that an ASHP needs a lot of air. The hot air from a small homebuilt solar air collector would probably blow through the ASHP in a few seconds, then start moving air through the collector at such a fast rate that it won't have time to heat up. I don't think you would even notice any difference in performance.

Having said all that; supplying warm air to an ASHP is a great idea. Raising the temperature even just couple degrees would help. If the heat pump runs for 10 minutes and you can supply warm air for only 5 of those ten minutes, you are still increasing performance.

It is possible to make a small solar air collector more effective. A small solar air collector doesn't have a lot of volume, but it has a lot of heat ~90*, so by using a simple "mixing valve" (basically a damper on the side of the duct that would go from the collector to the heat pump) would lower the temperature going into the ASHP to ~70* but with lots of volume.

The efficiency of a solar air collector is tied to the flow rate through the collector. It would be better to store the heat when the ASHP isn’t running and use the heat when the ASHP needs it. For example a solar green house. You could also use the solar air collector to heat a well-insulated large room and install the ASHP inside that room, venting the exhaust air outside. But the bottom line is- ASHPs need lots of air, which is where they collect heat from.

AC_Hacker · 12-26-11, 01:04 AM

Quote:

Originally Posted by Student 07

...I have been doing a lot of reading about air source heat pumps lately...

Sounds like you have been thinking a lot about this problem.

In my opinion, you are now at the point where asking other people for their opinion will not help you, because they simply don't know.

You have reached the point where you need to actually start trying out your ideas.

Find out for yourself which of your ideas are good ones and which of your ideas are not so good.

Experimenting with, and acting upon your ideas will make your thinking stronger.

If you do this, you will have more ideas, and better ideas.

It is time for the talking to stop and the action to start.

I invite you to start a thread on this forum...

Announce what is is you are trying to do, make a drawing of what you want to do, use you camera to illustrate to other readers what you have done.

Share your successes and failures in the forum.

I know that there will be great interest in what you are doing, from people who are also acting on their ideas, too.

I know because this is what we are all doing.

Welcome to the forum.

Act...

-AC_Hacker

08-28-11, 01:37 PM	#1
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	Solar air warmer for ASHP What if an ASHP was to draw air from a solar hot air collector? Has anyone tried this? As long as there is no air flow restriction then the slightly higher air temp would raise the HP's COP, while at worst it would be the same as with no collector. The collector could also have a bit of thermal mass, which would store some heat if the sun is shining while the HP is off. __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

08-28-11, 01:56 PM	#2
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	Pardon my ignorance, what is ASHP, HP and COP?

08-28-11, 03:27 PM	#4
iamgeo Apprentice EcoRenovator Join Date: Aug 2010 Location: Lakehills, Tx Posts: 168 Thanks: 4 Thanked 10 Times in 9 Posts	Thank you. Now I understand your question.

08-28-11, 09:21 PM	#5
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	you'd think the ASHP would "use up" the heated air from the collector quite quickly so you'd get minimal gain. Of course if your collector is massive then it's a different story. It's probably far easier to just feed the heated air into the building though. This way you can be gaining heat anytime the sun is shining not just when the sun is shining and the heat pump is running. Even on the coldest days mine doesn't run constantly. maybe 50% of the time

10-12-11, 09:25 PM	#7
solarman Lurking Renovator Join Date: Oct 2011 Location: MA Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	Hi, new to this so pardon my blunders. I've been toying with this idea for years, but never put anything together. Way I see it, solar heating panels give pretty good heat during peak sun, but we loose a lot earlier in the day or later in the afternoon. Also light clouds will put the output of a system to zero real quick. Adding an ASHP will do unbelieveable things, I think. During peak, shut down the HP, let the high gain of the panels do all the work. When the sun is low in the sky and the output is lower, turn on the HP using a closed loop system. Now the temperature of surface of the flat plate (or cans, downspout, whatever) will drop due to the colder return air. This raises the efficiency of the collector tremendously because the heat lost back to the atmosphere through the glazing is much less and the heat output jumps back up. Next benefit, the temperature of the air or water out of the HP will be higher than it is even in peak sun conditions, although there will most likely be less volume. This higher temperature will give you a higher gradient for pushing that last little bit of heat into the thermal mass you are using to store the heat. Sizing might be tricky, but I figure it all comes down to heat content. A 4'X9' flat panel in New England will recieve about 2900 Wattshours of energy from the sun at peak conditions. At 70% efficiency (number may be high but I've read claims of 80%) you get 2000 WattsHours, or just about 6,800 BTU per hour. At less than peak, an old 5000 BTU AC window unit would have the capacity to boost the efficiency of the system. Don't know a lot about refrigeration, but I suspect the design operating temperatures/pressures of an old 5000 BTU window system are quite different than what this setup would give us, so it would probably need modification of some sort. If anyone has built such a system and can comment, please do. I haven't found much written about such a combo system.

12-01-11, 12:12 PM	#8
menaus2 Apprentice EcoRenovator Join Date: Feb 2011 Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster Posts: 116 Thanks: 13 Thanked 35 Times in 25 Posts	I have a gas water heater that will need replacing soon, and I'm considering replacing it with a ASHP model. I also have a hot air solar panel that I could use (and prevent from self destructing or wasting the heat) during the summer months. Would running the 40 watt blower for the panel negate any efficiency gains given to the heat pump on the water heater? The panel is approx 3x16 ft. screen type with single layer polycarb glazing.

12-25-11, 05:25 PM	#9
Student 07 Helper EcoRenovator Join Date: Dec 2011 Location: Gresham OR Posts: 35 Thanks: 0 Thanked 3 Times in 3 Posts	Hi, I have been doing a lot of reading about air source heat pumps lately, I have had the same idea, and so here is what I found out. Air source heat pump (ASHP) water heaters have to be installed in a warm area like a basement. They suck warm air out of the basement and blow cold air out into the basement. They usually require a large room, more than 1000cubic feet. In my opinion they are kind of self-defeating, and the basement has to be heated to counteract the cold air from the HP. I think you are paying for the heat with this system. An ASHP pool heater gave some great information. They can be installed in an enclosed area that is heated, but the cold exhaust air should be vented to the outside to stay efficient. If the exhaust is vented out then makeup air has to be brought in. I don't know how many CFM an ASHP moves but I am sure it is a lot. The incoming air would have to be heated very quickly or have a very large source of warm air. If an ASHP water heater requires 1000 cubic feet of warm air: a 3 ton ASHP would need something significantly larger, like a large solar green house filled with warm air. Every time the ASHP turns on it would exhaust the warm air in the green house and refill it with fresh cold air which would have to be heated some before the heat pump turns on again. If you had a 10'x10'x10' solar greenhouse, it would contain 1000ft^3 of warm air. If the ASHP moved 350cfm, it would empty the greenhouse of its heat in ~3 minutes. Basically I am saying that an ASHP needs a lot of air. The hot air from a small homebuilt solar air collector would probably blow through the ASHP in a few seconds, then start moving air through the collector at such a fast rate that it won't have time to heat up. I don't think you would even notice any difference in performance. Having said all that; supplying warm air to an ASHP is a great idea. Raising the temperature even just couple degrees would help. If the heat pump runs for 10 minutes and you can supply warm air for only 5 of those ten minutes, you are still increasing performance. It is possible to make a small solar air collector more effective. A small solar air collector doesn't have a lot of volume, but it has a lot of heat ~90, so by using a simple "mixing valve" (basically a damper on the side of the duct that would go from the collector to the heat pump) would lower the temperature going into the ASHP to ~70 but with lots of volume. The efficiency of a solar air collector is tied to the flow rate through the collector. It would be better to store the heat when the ASHP isn’t running and use the heat when the ASHP needs it. For example a solar green house. You could also use the solar air collector to heat a well-insulated large room and install the ASHP inside that room, venting the exhaust air outside. But the bottom line is- ASHPs need lots of air, which is where they collect heat from.