Air to air heat pump in the attic?

orange · 06-26-11, 02:38 PM

Any advantage to this? Is the air volume too small? I just know that you have solar heat there as well as lost heat from the home.

New to this so go easy.

Xringer · 06-26-11, 10:57 PM

Unless you have a giant barn of an attic, or a VERY well ventilated attic,
or a very small ASHP, it's not going to work real well.

I'm kinda picturing a typical heating day in late December. It's totally overcast,
and any chance of solar gain is nil.

There is 6" of snow covering the entire roof, and it's 19 degs F outdoors.
The ASHP comes on and starts sucking the heat out of all the air in the attic.
The air coming out of the HP is 14 degs. After an hour, the air going into the HP is 14 degs.
Air coming out of the HP drops to 10 degs. After 1/2 hour, and so on..
Pretty soon, the attic is MUCH colder than it is outdoors.
Then you start wondering why the HP is in the attic..

The only way I can see good operation, is to monitor attic temperature.
Pause the HP, if the attic temperature drops below the efficient
operating range of the HP.
If the outdoor air is warmer, pump some into the attic.?.

Daox · 06-27-11, 08:15 AM

If you vented the outlet of the heat exchanger to the outside, it would probably work better. Of course, it would work much worse for cooling in summer if you intended it to do both heating and cooling.

AC_Hacker · 06-27-11, 01:20 PM

Quote:

Originally Posted by orange

Any advantage to this? Is the air volume too small? I just know that you have solar heat there as well as lost heat from the home. New to this so go easy.

Actually, your idea has some real merit.

Quote:

Originally Posted by Xringer

Unless you have a giant barn of an attic, or a VERY well ventilated attic, or a very small ASHP, it's not going to work real well.

Xringer has a fair-sized air source heat pump (I have a small one) and he has rightly noticed the huge volume of cold air that exhausts from the output of the "outside unit"... when he uses the phrase, "a giant barn of an attic" he is drawing attention to this. What he is really talking about is the total heat content of the attic air. If you live in an area where there is loads of sunshine on the roof in the winter, your total heat content could be right up there.

Here is a link to a brochure describing a house built in Portland, Oregon (my fair city). The house is called The Rose House, and it used extraordinary insulation and just about every other trick in the book to achieve "Energy Positive' status.

I mention this because it is very closely related to what you are considering. Notice in the above diagram, the roof detail to the upper left... That face of the roof is oriented to the south and gets maximum sun, so it is the logical place to put solar PV collectors. The Rose House uses the fact that considerable heat is lost from the underside of the PV panels, so that heat is captured by the input to the Air Source heat pump. This warmer air going into the ASHP raises the efficiency of the heat pump... This has an additional benefit, in that PV panels become less efficient as their temperature rises, and drawing air from the underside of the panels also cools them and raises their efficiency too. So it's a double win.

Daox also noticed:

Quote:

Originally Posted by Daox

If you vented the outlet of the heat exchanger to the outside, it would probably work better. Of course, it would work much worse for cooling in summer if you intended it to do both heating and cooling.

The Rose House deals with this too...

The Rose House certainly benefited from some very clever thinking, and is definitely food for thought.

Regards,

-AC_Hacker

orange · 07-01-11, 02:10 PM

Well,

I live near Vancouver which is pretty mild. I have never needed a A/C unit. Our house gets a lot of sun though.

I dont have a barn of an attic so perhaps the furnace heat pump would not be a good fit. The heat pump hot water tank could go there. I wonder if that would pass code.

Part of the reason for wanting to locate the hot water tank there as well, is that in effect, if you HW tank is in your home unvented, the heat pump is just stealing heat from your home to heat the water. Your electrical bill would go down put your gas bill up. In summer the cooling would be good though.

Thanks for your input. More to ponder.

Xringer · 07-01-11, 03:08 PM

Quote:

Originally Posted by orange

Well,
the heat pump is just stealing heat from your home to heat the water.

That's one of the main reasons I would not want a heat pump HW heater in my basement.

But, in the summer it would dehumidify the basement, and of course,
keep it cooler down there. (It's already like 21C down there, during summer)!

Anyways, I would not mind having a ASHP outdoors, to make my HW.
It would work great during the warm summer, and might even be useful
during the winter for some basement space heating.
(Assuming it was an inverter-type high-BTUh water heater).

orange · 07-03-11, 06:30 PM

I guess if you go through the trouble of venting a HWHP (just made that up) to the outdoors then it would be fine.

Quote:

Anyways, I would not mind having a ASHP outdoors, to make my HW.
It would work great during the warm summer, and might even be useful
during the winter for some basement space heating.
(Assuming it was an inverter-type high-BTUh water heater).

Do you mean that the heat pulled out of the home by the heat pump in summer is used to heat the HW? That's a great idea. I guess one day all this will be integrated. For now we have to do custom. Tricky stuff.

Xringer · 07-03-11, 08:22 PM

Yeah, it seems like installing an ASHP in the attic, but venting all it's output
into the outdoors would be a pretty good way to harvest solar heating
from the roof shingles and leakage from the warm rooms below the attic.
A good idea for those who don't care about the cooling function.
In the summer time, the efficiency would be at it's peak..

"Do you mean that the heat pulled out of the home by the heat pump in summer is used to heat the HW?
That's a great idea. I guess one day all this will be integrated. For now we have to do custom. Tricky stuff."

Yeah, it looks like a good idea. Pump the room heat into the hot water tank.

But what happens when the room is already too cool?
Or, the hot water tank is already at max temperature?

The user would have to run his AC with the doors and windows open,
if he wanted to take a shower that evening..

Integrated systems are being made.

Split Heating cooling hot water heat pump : Heat Pump|Europe Tech Best Price Heat Pump,Air Source Water Source Heatpump,Heat pump leading manufacturer

My DIY idea is to use the outdoor unit of a standard Sanyo mini-split,
with a heat exchanger (R410A to water) to heat my water using outdoor air.
Which can even be done during most of the winter. Especially during the
warmest part of the day.

I'm not sure just how hot the old Sanyo could get the water,
so plan-B would be to add a pre-heater tank to my current system.
So, instead of trying to heat 64F water, (with my oil burner), it would be
up around 80-120F.?. Much easier to heat then..

06-26-11, 02:38 PM	#1
orange frugal builder Join Date: Feb 2009 Location: Bowen Island, BC Posts: 16 Thanks: 0 Thanked 0 Times in 0 Posts	Air to air heat pump in the attic? Any advantage to this? Is the air volume too small? I just know that you have solar heat there as well as lost heat from the home. New to this so go easy.

06-27-11, 08:15 AM	#3
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	If you vented the outlet of the heat exchanger to the outside, it would probably work better. Of course, it would work much worse for cooling in summer if you intended it to do both heating and cooling. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

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06-26-11, 10:57 PM	#2
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Unless you have a giant barn of an attic, or a VERY well ventilated attic, or a very small ASHP, it's not going to work real well. I'm kinda picturing a typical heating day in late December. It's totally overcast, and any chance of solar gain is nil. There is 6" of snow covering the entire roof, and it's 19 degs F outdoors. The ASHP comes on and starts sucking the heat out of all the air in the attic. The air coming out of the HP is 14 degs. After an hour, the air going into the HP is 14 degs. Air coming out of the HP drops to 10 degs. After 1/2 hour, and so on.. Pretty soon, the attic is MUCH colder than it is outdoors. Then you start wondering why the HP is in the attic.. The only way I can see good operation, is to monitor attic temperature. Pause the HP, if the attic temperature drops below the efficient operating range of the HP. If the outdoor air is warmer, pump some into the attic.?.

07-01-11, 02:10 PM	#5
orange frugal builder Join Date: Feb 2009 Location: Bowen Island, BC Posts: 16 Thanks: 0 Thanked 0 Times in 0 Posts	Well, I live near Vancouver which is pretty mild. I have never needed a A/C unit. Our house gets a lot of sun though. I dont have a barn of an attic so perhaps the furnace heat pump would not be a good fit. The heat pump hot water tank could go there. I wonder if that would pass code. Part of the reason for wanting to locate the hot water tank there as well, is that in effect, if you HW tank is in your home unvented, the heat pump is just stealing heat from your home to heat the water. Your electrical bill would go down put your gas bill up. In summer the cooling would be good though. Thanks for your input. More to ponder.

07-03-11, 08:22 PM	#8
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Yeah, it seems like installing an ASHP in the attic, but venting all it's output into the outdoors would be a pretty good way to harvest solar heating from the roof shingles and leakage from the warm rooms below the attic. A good idea for those who don't care about the cooling function. In the summer time, the efficiency would be at it's peak.. "Do you mean that the heat pulled out of the home by the heat pump in summer is used to heat the HW? That's a great idea. I guess one day all this will be integrated. For now we have to do custom. Tricky stuff." Yeah, it looks like a good idea. Pump the room heat into the hot water tank. But what happens when the room is already too cool? Or, the hot water tank is already at max temperature? The user would have to run his AC with the doors and windows open, if he wanted to take a shower that evening.. Integrated systems are being made. Split Heating cooling hot water heat pump : Heat Pump\|Europe Tech Best Price Heat Pump,Air Source Water Source Heatpump,Heat pump leading manufacturer My DIY idea is to use the outdoor unit of a standard Sanyo mini-split, with a heat exchanger (R410A to water) to heat my water using outdoor air. Which can even be done during most of the winter. Especially during the warmest part of the day. I'm not sure just how hot the old Sanyo could get the water, so plan-B would be to add a pre-heater tank to my current system. So, instead of trying to heat 64F water, (with my oil burner), it would be up around 80-120F.?. Much easier to heat then..