Heating/Cooling units for residential houses 2

[BIPVguy]

Dear all,

I would kindly ask for your assistance please.
I am supposed to select appropriate heating/cooling strategy for luxury residential houses (130 sqm TFA each) located in a sea resort.

I am thinking of using small fan coil units.
What do you think about combination of underfloor heating and ceiling cooling?
Based on your experience, what would you prefer taking into account cost, efficiency,maintenance and thermal comfort ?

Thank you muchly.
Best Sasa

 

[willard3]

What do you mean by ceiling cooling? Radiant loops in the ceiling?

If you do this in a high humidity area (as in by the ocean) and don't treat the outside air before it enters the space, buy a ticket to Tierra Del Fuego. There will be lots of condensation and failure of building materials/finishes.

Radiant heating underfloor is a good system.

 

[AbbyNormal]

In the pacific northwest, the proximity to the ocean does not make it humid, other places a different story.

Radiant cooling is an accident waiting to happen, if ambient dewpoints are above say 18C

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

AbbyNormal- Well I guess the millions of sq. meters of radiant cooling systems in Europe and other parts of the world, including Bangkok Airport (if you want a hot and humid climate) are a risky venture. North America is about the only place I continually encounter the myths and legends about radiant cooling, and the unwillingness to even have a logical, rational engineering look at it as a viable system.

Yes, I completely agree that one has to be careful about dehumidification in hot and humid climates, but I think that's been pretty well licked by now, eh?

Check out Stan Mumma's tests on radiant cooling panels where he ran them down to 14F below the ambient dewpoint, and how long it took before visible drops were seen on the panel surface:

http://doas-radiant.psu.edu/DOAS_RADIANT_HONOLULU_TP4573.pdf

http://doas-radiant.psu.edu/cond_control_fall_03.pdf

http://doas-radiant.psu.edu/Journal2.pdf

Here is one link to the Bangkok Airport radiant cooling system:

http://www.transsolar.com/download/e/TRANSSOLAR Concept for the NBIA.pdf

A Google search on "radiant cooling" yields a ton of material, and it's a mainstream cooling system in many parts of the world, and is as common as VAV reheat systems in North America.

 

[BIPVguy]

Dear all,

Thank you on your useful comments.
I quite agree with GMcD. Radiant heating/colling is quite popular on Europe.

I would say it is more expensive than other systems and problems with condensation might occur but almost ideal air temperature distribution in a zone is achieved resulting in improved thermal comfort.Moreover, set point temperature can be lower as enclosures (walls, floor, ceiling) are at higher temperature. Finally, problems associated with dust circulation could be avoided as heat is mostly transferred via radiation.

Thanks Sasa

 

[trashcanman]

Most interesting. Where does the condensate go?

 

[GMcD]

Trashcanman- What condensate?? The whole point to a properly applied radiant cooling system is to dehumidify the air being supplied/circulated in the space to prevent condensation. The drier the climate, the less dehumidification you need, and if the room cooling loads are low enough, you don't need to run the radiant cooling surface lower than 65F-66F. Basically the air side of the room comfort system is reduced to supplying the required fresh air for ventilation, and de-humidifying it on the way by, and not having to size the air system for both sensible and latent cooling. The air system is relegated to just latent cooling, while the radiant cooling system does the sensible cooling.

Now chilled beams- those ARE, in many cases designed to be near the dewpoint and condensation regime, and do have condensation collection means in them.

Don't forget- no one here is advocating radiant cooling as the "sole" means of room cooling- you have to have all three legs of the human comfort stool: fresh air for ventilation, humidity control in humid climates, and radiant heat exchange control. ASHRAE-55 Standard.

 

[GMcD]

BIPVguy- to get back on topic- the appropriate mech systems, even for resort McMansions (totally unsustainable waste of energy and materials, but just my opinion) - the envelope is the primary comfort system in the building- well insulated walls and roof with minimized thermal bridging, and good exterior overhangs and/or solar control, along with window units suitable for the local climate - cooling dominated vs heating dominated. Not knowing the location for these resort buildings makes it diffcult to add more info - but stick with the basics - good envelope and solar control as required for the local climate, passive natural ventilation if appropriate for the local climate, harvest the local natural energy at the climate location and squeeze as much passive comfort systems out of the building design as possible before resorting to active mechanical solutions, like some heat recovery ventilators/energy recovery ventilators, and radiant heating/cooling. If combined radiant heating and cooling is going to be used, then consider the ceiling surface as the primary active radiant surface - no furniture masking, no carpets or other floor insulators to get in the way. Then maybe use some limited in-floor heating-only floor warming in hard tile floors like bathrooms and kitchens.

The first step is to "climate adapt" the building design, and reduce the heating/cooling loads down as far as possible. Then look at active comfort systems.

 

[AbbyNormal]

GMCD, we have discussed radiant cooling in other forums.

In a dry climate like Europe, and in places where the ambient dewpoints do not hit 64F, like coastal British Columbia it would be a great system.

In places where the ambient dewpoint is 80F, it is a disaster waiting to happen. Might as well take the mentality that you do not have to insulate air conditioning ducts as long as they are run in the conditioned space.

You could not pay me enough to specify a system creating a 64F ceiling here. The underside of this decking was 78F when a couple tropical storms went by.

So you want to use radiant cooling in a humid environment, knock yourself out, it is like rebuilding the 9th ward and saying, we are good as long as the dykes do not fail.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

Abbynormal - using photos of poor envelope and bad design practices (open ceiling plenum returns and crappy infiltration) isn't a good argument. There's no way radiant cooling will work with bad bulding envelope design, just like ceiling plenum returns won't work with a bad roof design. "Dry climates like Europe" - another cop-out- there are plenty of climate zones over there where the summer outdoor wet bulb is over 70F, and check the climate data for Winnipeg Manitoba for summer design (74F/75F wet bulb) where a 610,000 SF radiant slab cooling system is being built as we speak. If Bangkok Airport isn't a good enough example, then we'll agree to disagree and I'll continue to design and specify low energy radiant systems to my hearts' content. They are simple, and they work. There is a lot more integrated and coordinated design effort required for applied radiant systems, but I got tired of picking packaged HVAC units out of catalogues a long time ago.

I can understand people being risk-averse, but isn't our jobs as engineers to design things to minimize that risk with known best practices? The North American HVAC industry has become a reactive bunch- let a crappy building envelope design get "fixed" by applying mechanical HVAC solutions to them, and the cheaper, the better. Since when did efficient = cheap?

 

[AbbyNormal]

It is an accident waiting to happen. If something goes wrong, like a DOAS fails, dehumidifier does not work, the results will be disasterous.

The analogy of New Orleans is perfect. It's built below sea level, and will be perfectly safe as long as the levees hold and the pumps do not fail. But they have failed, and will fail again.









Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

AbbyNormal: And it's so hard to put an interlock and a condensation sensor to shutdown or reset the radiant cooling water upon DOAS failure or ambient wet bulb going beyond setpoint? There are more complicated controls for VAV reheat systems, and those are mainstream. All of the caoillary tube sheets used in Europe come complete with a condensation sensor in the tube sheets wired through the local thermostat and DDC system. No Sweat, literally.

 

[GMcD]

Darn- I wish this forum would allow editing- the word is "capillary" in my post above. Capillary tube links:

http://karosystemes.com/eng/cooling_radiant/present.htm

http://www.plasticmagen.com/16/

http://www.bekausa.com/

 

[AbbyNormal]

That photo was not the result of a poor envelope construction. That photo was the result of applying techniques successful in dry climates in a humid climate. When it went wrong , it went very wrong.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

AbbyNormal: Dry climate techniques in humid climates - isn't that a comment on the level of education of building design "professionals"? I find that the level of education for HVAC designers and engineers in North America doesn't provide anywhere near a good enough education in HVAC and Building Science/Building Physics design to allow them to be safe desiging outside their own city limits. Buildings have to be "climate adapted", and if the HVAC designer doesn't understand the climate he's designing for, then it doesn't matter what kind of HVAC system they design, it'll go off the rails, let alone radiant cooling. It's why guys like Joe Lstiburek have to publish the "Top Ten" lists of what NOT to do in different climates.

 

[AbbyNormal]

It is a comment on owners recycling a successful design for Arizona in the Tropics.

You should read Joe's number one dumb thing to do in the South, you are personifying it.

Radiant cooling has no place down in the tropics, will work great in low dewpoint places like BC, Europe, but is, and will remain to be, a big accident waiting to happen in a humid environment.

How do you avoid dykes failing and filling the 9th ward like a goldfish bowl, you bring in 5 trillion yards of fill to elevate it. Or build new dykes good until the next big one.

How do you avoid a catastrophic condensation problem? By not maintaining ceilings 15 degrees below the ambinet dewpoint.

Go read the Florida Solar centre a bit, one of their biggest comments is to tell home owners to not set the thermostat below 78F. The minor reason is it saves money on operating costs, but the major reason is, it is not below the ambient dewpoint.

Traditional homes here, without air condtioning never had mold because there were no surfaces colder than the ambient dewpoint.

Air condition a framed home here and now you are maintaining a space a FEW degrees below the dewpoint. Constant infiltration can then become problematic.

Now you want to promote a radiant ceiling a good 15 degrees below the ambinet dewpoint in a home, that is IDIOTIC. A house is going to have all the pressurization and safeguards that an airport terminal pressurized to keep jet fumes out will? I don't think so. Joe homeowner is going to add "condensation detectors" on his ceiling, or have safety controls to shut your cooling off if RH rises? Why have the POS system in an application it has no business in, in the first place.

Use it in dry Europe, coastal BC, a hospital in Canada where it belongs.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

AbbyNormal: Quote: "Now you want to promote a radiant ceiling a good 15 degrees below the ambinet dewpoint in a home, that is IDIOTIC. A house is going to have all the pressurization and safeguards that an airport terminal pressurized to keep jet fumes out will? I don't think so. Joe homeowner is going to add "condensation detectors" on his ceiling, or have safety controls to shut your cooling off if RH rises? Why have the POS system in an application it has no business in, in the first place."

Whoa, whoa whoa. You and I don't disagree- I am NOT "promoting" radiant cooling in an application where there are significant risks- risk number one being the expertise of the building design team and the installers in a hot and humid climate. All I am promoting is that radiant cooling has a place in the low energy building systems toolkit, and it has to be applied correctly, and that there are common, reasonable "good practice" safeguards to reduce the risk to be no different that a correctly designed and installed "all-air" system. I am not saying it should be a mainstream application in the Bahamas or Costa Rica - one can design a low energy building comfort system there quite easily without radiant cooling.

I used the Bangkok Airport and Winnipeg Building as examples of radiant cooling in a hot and humid climate just to illustrate that it can be made to work in an extreme climate. There has been no information yet from Bipvguy about his specific location of where he is designing these McMansions, so he may, in fact be in a location where ambient dewpoint excursions don't go to high levels like they would in the SE US zones.

What I AM promoting is climate adapted design, and to design the building to conform to the local climate and lower the cooling and heating loads as far as possible by relying on passive building design, THEN apply suitable mechanical systems that ARE APPROPRIATE FOR THE LOCAL CLIMATE.

I take issue with folks who dismiss radiant cooling right away due to the extreme blanket comments that get made like the ones above. Radiant cooling doesn't have to be set at 63F to 65F to "work". All you need is large surface areas to be kept a a few degrees below what you want for comfort - in a hot and humid climate, a radiant surface kept at 74F-75F can provide comfort if the ambient room "operative temperature" for comfort only needs to be in the 77F to 78F range. Large surface areas at small delta T's to the room can provide significant cooling effect. When you consider that the average surface temperature of the average human is 85F, any surrounding surface cooler than that will provide "radiant cooling" anyway.

What are the average floor surface temps inside the tropical houses at mid-day where they are slab on grade and "ground-coupled" - ie- no insulation under them?

 

[AbbyNormal]

If a home is kept at a constant temperature, I would estimate the floor to be 1F warmer than the air 5 feet above it.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

Why not actually measure the bare floor temps/tiled floor surface temps with an infrared surface temperature thermometer? I will bet that it will be a few degrees below ambient during most of the day as long as it's not exposed to direct sunlight. Surface temperature readings around the room and especially the perimeter walls and ceilings can reveal a lot about the envelope and the mean radiant tempertaures of the room.

 

[AbbyNormal]

I measured it with an infrared last night. The stat on the wall had a surface temp of about 75, the floor about 76.

tap water is about 81 or so this time of year, the pipes are underground

Take the "V" out of HVAC and you are left with a HAC(k) job.