Whole House Fan - So far so good.

[UncleDave]

Whole house fans generally speaking are a bad idea. They waste energy by sending conditioned air into the atmosphere and suck in humid (obviously not applicable in a desert) outdoor air. They also leak conditioned air.

There are more and less sensible ways to use them for sure.

"Waste" air conditioning... why would anyone run their air conditioner and a whole house fan? This criticism makes little sense to me.

They aren't really great for humid environments, but if you have no AC, and no way to fight humidity anyway you're probably better off with fans in the window and inside.

 

[PimTac]

They aren't really great for humid environments, but if you have no AC, and no way to fight humidity anyway you're probably better off with fans in the window and inside.

Definitely. Air movement is still key. Even with air conditioning running we had stand fans blowing to make it more comfortable. We could raise the temperature setting on the A/C remote to conserve energy.

 

[UncleDave]

FSEC-PF-273-92

Information on the renewable energy and energy efficiency research, education, training, and certification activities of the Florida Solar Energy Center (FSEC)

www.fsec.ucf.edu

Above is a study, Florida-based, of whole house fan cooling.
They were more popular before air conditioning became common.

Good article.

 

[UncleDave]

Definitely. Air movement is still key. Even with air conditioning running we had stand fans blowing to make it more comfortable. We could raise the temperature setting on the A/C remote to conserve energy.

This is exactly why I have ceiling fans in every room, and a giant one in the living room.

 

[brianl703]

Attics in Texas get miserably hot, and it would seem counterintuitive to put in the HVAC air handler up there, but that's where mine is.

I read a report that showed that putting an HVAC air handler in an attic increases the heat load on the unit by 6000BTU, or half a ton.

My old house, just the upstairs ducts were in the attic, and I could tell that was a miserable energy waste by the 30 seconds of hot air it blew during the summer, and the 30 seconds of cold it blew during the winter.

 

[UncleDave]

I read a report that showed that putting an HVAC air handler in an attic increases the heat load on the unit by 6000BTU, or half a ton.

My old house, just the upstairs ducts were in the attic, and I could tell that was a miserable energy waste by the 30 seconds of hot air it blew during the summer, and the 30 seconds of cold it blew during the winter.

Ive seen articles that say the same and it makes tons of sense - question is - where do you put the ductwork and handler if not in the attic?

 

[brianl703]

Ive seen articles that say the same and it makes tons of sense - question is - where do you put the ductwork and handler if not in the attic?

Assuming a house with a basement:

Air handler in basement, ductwork in basement ceiling to serve first floor and basement, and if 2nd floor, ductwork above 1st floor ceiling to serve 2nd floor via floor registers (and a chase between 1st and 2nd floors for the supply and return).

Assuming a two-story house on a slab or crawlspace:

Air handler in closet on 1st floor, ductwork in space above 1st floor ceiling, with ceiling registers for 1st floor and floor registers for 2nd floor.

Assuming a single-story house on a crawlspace:

Air handler in closet, ductwork in crawlspace

Assuming a single-story house on a slab:

Air handler in closet, ductwork embedded in slab (I have never personally seen this, but I've seen pictures and videos of it). OR ductwork placed in soffit below ceiling

 

[UncleDave]

Assuming a house with a basement:

Air handler in basement, ductwork in basement ceiling to serve first floor and basement, and if 2nd floor, ductwork above 1st floor ceiling to serve 2nd floor via floor registers (and a chase between 1st and 2nd floors for the supply and return).

Assuming a two-story house on a slab or crawlspace:

Air handler in closet on 1st floor, ductwork in space above 1st floor ceiling, with ceiling registers for 1st floor and floor registers for 2nd floor.

Assuming a single-story house on a crawlspace:

Air handler in closet, ductwork in crawlspace

Assuming a single-story house on a slab:

Air handler in closet, ductwork embedded in slab (I have never personally seen this, but I've seen pictures and videos of it). OR ductwork placed in soffit below ceiling

No basements in cali.

Assuming a two-story house on a slab or crawlspace:
Air handler in closet on 1st floor, ductwork in space above 1st floor ceiling, with ceiling registers for 1st floor and floor registers for 2nd floor.

Ok I build an enormous closet on the first floor - what space above the 1st floor ceiling? There is no space to run ducts between floors?

Putting ductwork in the crawlspace would make you unable to crawl to the locations you may need to go - cool idea but unless you have an elevated house I just dont see it?

In order to avoid the handler and ducts in the attic you pretty much have to build the house aound the HVAC like the ducts in slab as you mentioned.

Mini splits mostly avoid ductwork and attic heat loss.

 

[brianl703]

No basements in cali.

Assuming a two-story house on a slab or crawlspace:
Air handler in closet on 1st floor, ductwork in space above 1st floor ceiling, with ceiling registers for 1st floor and floor registers for 2nd floor.

Ok I build an enormous closet on the first floor - what space above the 1st floor ceiling? There is no space to run ducts between floors?

Sure there is. With the use of 2x10 floor joists (which I think is the minimum size allowed), you have plenty of room for ducts, though you'll likely need a soffit at one end for the trunk duct. With the use of I-joists you can run the trunk duct through the joists, as was done in my house.

(And the same is true for a crawlspace, those floor joists will accommodate ductwork between the joists, keeping it out of the way).

Yes, you do have to design the house to accommodate the duct work, if you won't want it in the attic, but it's not impossible or even uncommon.

The builder of my house even specifically stated in their "Why our homes are more energy efficient" brochure that they don't install any HVAC equipment or ducts in the attic.

 

[brianl703]

No basements in cali.

Assuming a two-story house on a slab or crawlspace:
Air handler in closet on 1st floor, ductwork in space above 1st floor ceiling, with ceiling registers for 1st floor and floor registers for 2nd floor.

Ok I build an enormous closet on the first floor - what space above the 1st floor ceiling? There is no space to run ducts between floors?

 

[ecotourist]

FSEC-PF-273-92

Information on the renewable energy and energy efficiency research, education, training, and certification activities of the Florida Solar Energy Center (FSEC)

www.fsec.ucf.edu

Above is a study, Florida-based, of whole house fan cooling.
They were more popular before air conditioning became common.

It would be possible to jury rig a version of this approach by building a box around a fan which then would be inserted into the attic access port, with the cord hanging down and plugged in somewhere in the room below. The fan would be oriented so as to blow air into the attic.

We don't have much of an overheating heating problem at our present location, as it cools off quite dramatically here at about sundown, and simply opening windows on the lower and upper floors at the end of the day cools things off very nicely. We leave this passive ventilation system on all night and only close up the house again in the morning when the inside and outside temperatures equal (usually about 10:00 am). The house then stays fairly cool all day. By using this passive cooling system we have only needed to use our heat pump for cooling a total of about 5 days in 6 years.

 

[UncleDave]

View attachment 113447

I should have been more specific - in terms of a retrofit there's no way to do that.

This is effectively building the house around the AC - very nice.

 

[UncleDave]

Sure there is. With the use of 2x10 floor joists (which I think is the minimum size allowed), you have plenty of room for ducts, though you'll likely need a soffit at one end for the trunk duct. With the use of I-joists you can run the trunk duct through the joists, as was done in my house.

(And the same is true for a crawlspace, those floor joists will accommodate ductwork between the joists, keeping it out of the way).

Yes, you do have to design the house to accommodate the duct work, if you won't want it in the attic, but it's not impossible or even uncommon.

The builder of my house even specifically stated in their "Why our homes are more energy efficient" brochure that they don't install any HVAC equipment or ducts in the attic.

a mini split with zero ductwork is likely the most efficient in terms of BTU of cooling delivered per watt.

 

[brianl703]

a mini split with zero ductwork is likely the most efficient in terms of BTU of cooling delivered per watt.

Doesn't work very well if you have a lot of rooms. And current building codes require that ducts be sealed with duct mastic (which has been standard in commercial construction for decades, but was almost never done in residential construction).

Always wondered how much the ducts in my old house were leaking into the attic...

 

[brianl703]

This is effectively building the house around the AC - very nice.

Central air has been around for decades now, why would any builder NOT do that???

 

[PimTac]

a mini split with zero ductwork is likely the most efficient in terms of BTU of cooling delivered per watt.

Doesn't work very well if you have a lot of rooms. And current building codes require that ducts be sealed with duct mastic (which has been standard in commercial construction for decades, but was almost never done in residential construction).

Always wondered how much the ducts in my old house were leaking into the attic...

At the house I have mentioned we installed mini splits. There are six units since we have multiple rooms. The setup has worked well because we selected units with sensors that detect when a person has left the room. The units spin down to a efficient setting and after a period of time turn off. Rooms like bedrooms are off during the day but will be occupied during the hottest part of the day sometimes. These are all inverter units as well.

 

[UncleDave]

Doesn't work very well if you have a lot of rooms. And current building codes require that ducts be sealed with duct mastic (which has been standard in commercial construction for decades, but was almost never done in residential construction).

Always wondered how much the ducts in my old house were leaking into the attic...

Im not sure about not working well, but I can say its pretty expensive and you have to find a place for the compressors.

My setup was completely redone just a few years ago with new ductwork, it seems pretty good.

 

[UncleDave]

At the house I have mentioned we installed mini splits. There are six units since we have multiple rooms. The setup has worked well because we selected units with sensors that detect when a person has left the room. The units spin down to a efficient setting and after a period of time turn off. Rooms like bedrooms are off during the day but will be occupied during the hottest part of the day sometimes. These are all inverter units as well.

Which brand? Ive used the mitsubishi and fujitsus and was pretty impressed.

 

[UncleDave]

Central air has been around for decades now, why would any builder NOT do that???

Thats a good question, Ive never been in a house in Cali built like that pict.
I had a friend buy a house in Sa Fran for 2.5M that has no air conditioning at all.

 

[WylieCoyote]

I read a report that showed that putting an HVAC air handler in an attic increases the heat load on the unit by 6000BTU, or half a ton.

This would explain why the 4 ton unit runs all day non-stop to keep 2000 square feet cool. It really should be a 4.5 or 5 ton.