Heat Pump Placement and Effects on Surrounding Air Temperature

elsedgwick · 02-19-14, 09:54 AM

I am having a dual-function Mitsubishi multi-split system (MXZ8B48NA condenser) installed as part of renovations. The house is an old frame house on brick piers and the back end is well off grade (~5.5 feet), and the air circulation around and under the house is good.
In the cooling-dominated climate of North Florida, I was considering putting the condenser under the house, figuring that the deep shade would keep that area slightly cooler in summer (as well as keep it out of sight and save space for landscaping). Does anyone see any issues with this? Will the air under the house just get heated to the point where the advantage from the deep shade is lost? Would dust from this area significantly shorten the lifespan or lessen efficiency?
Also, I'm having a hard time finding data on just how significantly a heat pump changes the temperature of the surrounding air. Anyone know of any resources? Another potential location would be slightly uphill (8-10 feet) from a citrus tree, but I wouldn't want to place it there if it would drop the local temperature by a few degrees in winter.
Thanks for your replies.

pinballlooking · 02-19-14, 10:12 AM

I am no HVAC expert at all but I can tell you that condenser will use up that cool air under the house in no time. Then it will bring in hot air from outside under your house. Unless your house is built on stilts like at the beach then it would work pretty well.

Daox · 02-19-14, 10:15 AM

What you could do is use the condenser to pull air through the underside of the house. This would use the coolness, but not heat up the air under the house. So, you would install a vent on one end, and have the condenser on the other end and pull air through.

elsedgwick · 02-19-14, 12:06 PM

Thanks for your quick responses.

The house is effectively on stilts - not 6x6s, as you see in beach houses, but brick piers that are about 6x12" and spaced every ten feet or so. And not raised as tall as a beach house - again, about 5.5' off the ground in back, where the unit would be located.

So are you suggesting against doing this, due to the fact that it would pull warmer air under the house (it doesn't matter that the unit is then operating in this warmer air, since that is what it would be doing, anyway, but presumably there is some migration of heat from the space under the house to the conditioned area), or are you suggesting that there just isn't much benefit?

jeff5may · 02-19-14, 05:14 PM

I would not want it blowing "opposite" air under the house. If you could get the outdoor unit to pull "shady" air, it would help somewhat. The newer mini splits are pretty flexible with temperature anyway. That being said, the closer you can get the supply air to room temperature the better they will save energy.

Most outdoor units shoot for ten degrees F or more of temperature shift.

AC_Hacker · 02-19-14, 08:12 PM

Quote:

Originally Posted by elsedgwick

Also, I'm having a hard time finding data on just how significantly a heat pump changes the temperature of the surrounding air. Anyone know of any resources?

I volunteer to be a resource...

My mini-split is located next to my front door, which in hind-site might not have been the best place... not the very worst place, but not the best either.

I've been seeing temperature differences of maybe 4 degrees F, both heating & cooling. But it's always 4 degrees in the least comfortable direction. So, on a hot day, I gotta walk through 4 degrees of even hotter air to get into the cool house... and oppositely so in the winter.

So you don't have snow to worry about, do you?

I just bet that you have a predominately prevailing wind direction, don't you?

If it were me, I'd put the outside unit toward the outside edge of the house, away from the direction of where the prevailing wind blows from. That way, you will get the maximum cooling from the space under the house, AND your exhaust air will be carried away, before it has any chance to build up.

And, I think your idea to put the unit under the house is a great idea. Just make sure that you allow easy access (including headspace) in case you need to clean the coils of any crud, or to service it in any other way.

You forgot to enumerate the advantage that 'out of sight is out of mind' with regards to security.

But make sure to mount it up just a bit from the ground to reduce the exposure to airborne dust.

Best,

-AC_Hacker

02-19-14, 09:54 AM	#1
elsedgwick Lurking Renovator Join Date: Feb 2014 Location: North Florida Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	Heat Pump Placement and Effects on Surrounding Air Temperature I am having a dual-function Mitsubishi multi-split system (MXZ8B48NA condenser) installed as part of renovations. The house is an old frame house on brick piers and the back end is well off grade (~5.5 feet), and the air circulation around and under the house is good. In the cooling-dominated climate of North Florida, I was considering putting the condenser under the house, figuring that the deep shade would keep that area slightly cooler in summer (as well as keep it out of sight and save space for landscaping). Does anyone see any issues with this? Will the air under the house just get heated to the point where the advantage from the deep shade is lost? Would dust from this area significantly shorten the lifespan or lessen efficiency? Also, I'm having a hard time finding data on just how significantly a heat pump changes the temperature of the surrounding air. Anyone know of any resources? Another potential location would be slightly uphill (8-10 feet) from a citrus tree, but I wouldn't want to place it there if it would drop the local temperature by a few degrees in winter. Thanks for your replies. Last edited by elsedgwick; 02-19-14 at 12:07 PM..

02-19-14, 10:15 AM	#3
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	What you could do is use the condenser to pull air through the underside of the house. This would use the coolness, but not heat up the air under the house. So, you would install a vent on one end, and have the condenser on the other end and pull air through. __________________ 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.

02-19-14, 10:12 AM	#2
pinballlooking Super Moderator Join Date: Jun 2013 Location: SC Posts: 2,923 Thanks: 172 Thanked 564 Times in 463 Posts	I am no HVAC expert at all but I can tell you that condenser will use up that cool air under the house in no time. Then it will bring in hot air from outside under your house. Unless your house is built on stilts like at the beach then it would work pretty well.

02-19-14, 12:06 PM	#4
elsedgwick Lurking Renovator Join Date: Feb 2014 Location: North Florida Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	Thanks for your quick responses. The house is effectively on stilts - not 6x6s, as you see in beach houses, but brick piers that are about 6x12" and spaced every ten feet or so. And not raised as tall as a beach house - again, about 5.5' off the ground in back, where the unit would be located. So are you suggesting against doing this, due to the fact that it would pull warmer air under the house (it doesn't matter that the unit is then operating in this warmer air, since that is what it would be doing, anyway, but presumably there is some migration of heat from the space under the house to the conditioned area), or are you suggesting that there just isn't much benefit?

02-19-14, 05:14 PM	#5
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	I would not want it blowing "opposite" air under the house. If you could get the outdoor unit to pull "shady" air, it would help somewhat. The newer mini splits are pretty flexible with temperature anyway. That being said, the closer you can get the supply air to room temperature the better they will save energy. Most outdoor units shoot for ten degrees F or more of temperature shift.