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I'm in the design process for a building. It has four rooms under the same roof but with breezeways between them for isolation purposes. There is no air exchange between the rooms, by design. The average room size is about 12 X 12.

I need to put in an efficient and inexpensive HVAC system. The two ideas so far are a mini-split and individual (four) room-sized heat pumps.

The lowest temperature I've ever seen here is 14 F, which froze everybody's pipes a few years ago. That is rare though; last winter we had a few nights in the mid-to-low 20s.

The high temperatures are generally the problem; this past summer we had 75 days over 100 F, and the intensity of the sun is, well, intense.

Here are the criteria:

available commercially
not costly
unit is not subject to becoming moldy (many high SEER AC units have internal pools of water that encourage mold)
zero air exchange between the rooms
failure of HVAC for one room does not affect HVAC for the other rooms

The idea of the four heat pumps came from the requirement that the rest of the house still be livable even if one room develops a problem. That is also why the rooms are isolated and why there is no duct work.

Engineers? Creative people?

MA

MaryAnn wrote: not costly

How not costly? The place we stayed at near Austin last week had a Mitsubishi heat pump setup, which (from what I see online) would run $2-3 K. Per unit - naturally there's no economy of scale if each unit must be completely independent.

Our hosts were pleased with it, but it just went in, and they haven't really been depending on it for long. They have more experience with the cooling feature, and that seems to have worked well. We got more experience with the heating feature, which ... might have worked well if it had been set up properly.

I'm guessing that a window or through-the-wall combination AC/electric heater would be both cheap, independent, and would do both the jobs in room that small. Not so cheap as natural gas, but cheap at install.

Do the four systems need to be separately metered?

Is there a basement underneath?

Does each room have its own bathroom?

is there a kitchen?

Do the four systems need to be separately metered?
No, they are all part of the same house.

Is there a basement underneath?
No.

Does each room have its own bathroom?
One of them has a bathroom.

is there a kitchen?
The kitchen is one of the rooms. The others: a mud room/bathroom, and two bedrooms.

(off the off topic: I see I once again have got to six valves. I wonder if it will all disappear again as it did before?)
MA, who doesn't have enough fingers on one hand to use six valves.

Since you are building new, first make sure everything has great insulation. That new foam stuff will work good especially with 6" walls. This will also strengthen the structure a lot. Next, consider a central ground sourced heat pump. These will work down to -40 F and are the best air conditioners. These are expensive to install, but you do get a substantial tax rebate (like 30%). They are 300% efficient so they run cheaply overtime. (great pay back). The issue of isolation of each room is a challenge but could be done if you use windows, vents and a water system as a-posed to forced air. I have one of these in Minnesota and they work great.

Second to Brian's comment re insulation. There is a saying that you pay for insulation whether you have it or not. Bloke's comment re performance of heat pumps is generally true. Most manufacturer's claimed outputs for my part of the world are given for +7C (45 F) and performance does definitely drop with the outside temperature. However, Mitsubishi Electric do offer a range of units here that they have rated to -15C (also -15F). Not sure how they do it as it seems to be counter to the laws of thermodynamics, but if they were to provide a written guarantee, then maybe...

I don't like putting indoor units in kitchens, because they do tend to get a bit messed up sucking in stuff in the air while cooking. And we like to position outdoor units where they can catch some morning sun if we can.

Hope this helps
Andrew

Insulation will be a bit of a problem; I have to be able to use a blow torch on all surfaces to sterilize them, I haven't been able to figure out how to insulate it. The walls will be concrete-filled dry stack; we're planning a metal ceiling with panels that can be lifted out of a frame, with insulation just sitting on top of them. Any other ideas?

MA

I'm not sure if I'm game to ask what you are intending to do in these rooms... Oh well, I guess I have. For that level of cleaning I'm thinking some sort of commercial food processing? In which case I would suggest you look at coolroom panel for your room construction. Basically polystyrene foam sandwiched between colorbond steel. Varying thicknesses of foam available but 3" should be adequate. Gives a nice smooth interior finish for cleaning. I know of one manufacturer here in Aus that is offering a type of veneer finish on outer surfaces similar to laminate timber flooring, so that they can provide a quite realistic stone finish to outside. Windows and doors can be quite easily cut in as required.

Cheers
Andrew

I think in principle there isn't any reason insulation couldn't go on the outside of a concrete wall. You'd need a shell outside that, maybe something like corrugated steel. It makes enough sense to me that I wonder if it may be common down there - you get protection from external temperature extremes and direct insolation, while the concrete is where it belongs for thermal mass.

For the roof, I see there are coatings that claim to be as good as insulation, e.g. Diamond Seal. Have no idea how much that stuff costs.

What it's for: to live in. The reason for the amazing level of cleanliness required is that I lived for many years in a water damaged building (hidden toxic mold inside a wall,) have the genetic makeup that goes with dire consequences, and can no longer spend significant time inside any building at all (Ended: all indoor musical participation; Sold: all tubas.) I've lived outside for more than a year and am getting REALLY tired of that; if I were 33 instead of 63 it might not be so hard. Communication with like people has taught me that extreme avoidance is the only solution, and most of them continue to live outdoors or in buildings they have constructed with the same attention to being able to sterilize them. You have not met these people because they are living outside in the desert somewhere.

The reason for the total isolation between rooms is so that if one becomes contaminated, there will be another I can live in while I'm trying to sterilize the first one.

If you're curious (most people are not) it's all at:
http://www.survivingmold.com" target="_blank (but not all lives can be restored, no matter what he claims)

MA

Wow, I can honestly say that possibility hadn't crossed my mind. Guessing you would rather not have colorbond walls in your living areas. Had a quick look through the site you linked but didn't notice any particular mention of HVAC solutions for your situation. However, I would think that the right HVAC setup could have a significant impact on your quality of life.
May I suggest you check the following forum : http://hvac-talk.com/vbb/forum.php" target="_blank and see what that may turn out. There are some top quality sounding operators on that site and may be able to assist in finding a local expert who can assist with your particular requirments. Off the top of my head, I'd be tossing up between sealing up really tight and providing high levels of filtration to clean the air, or maybe keeping it wide open (closer to living outdoors) but that increases your heating and cooling loads significantly.

Good luck!
Andrew

Just a suggestion for what to use on the walls and ceilings ... Why not use FRP ( http://www.frpshop.com/" target="_blank" target="_blank ) . It's used in commercial kitchens particularly in the dishrooms. It's non pourus and the seams can be sealed between each sheet. You won't have to use a blowtorch to sterilize it. You can use a water hose and bleach,soap, quaternary sani and or whatever else you what. I've seen some restaurants even power wash thier FRP walls. If you haven't already made this building you can put in floor drains to remove all of the water.
FRP can be installed on sheetrock or plywood so you can nail wooden studs to the concrete wall,nail the sheetrock or plywood to the studs and insulate behind it. It can be nailed or glued down though I think it's best to do both.

tastuba wrote:However, I would think that the right HVAC setup could have a significant impact on your quality of life.

Of course, the flip side of that is that the wrong HVAC setup could also have a significant impact. Especially the AC side, which by nature would tend to have large inaccessible surface areas that might tend to get damp.

I'd gamble on all-out `passive' thermal design for the buildings, if only because it's more cost effective to start there, than try to retro-fit later if the AC can't be made to work. I'm sure you already have lots of info on this stuff, but e.g., http://www.azsolarcenter.org/tech-scien ... oling.html looks like it covers a lot of the basics. You already have the masonry interior. The cluster of small separated units is an unusual constraint that might be an interesting question for an expert. My intuition says it might be to your advantage, because the greater per volume surface area will exert a greater effect on the interior. Depending perhaps on how you control air flow through the breeze way over the day, if it can be shut off to some degree when the air is hotter than the outside of the wall (or colder in the cold part of the year.)

Trees are big deal, but of course need water. Our friend in Tucson piped grey water out to the trees.

And now, for something completely different - Arizona Daily Star article about a Tucson home made from steel shipping containers. Cheap, strong, durable, modular. This one looks like 4 units put together for 1280 square feet.

Anyway - if you get something up, please keep us posted! Pictures would be good.