Radiant Ceiling Heating/Cooling

GMcD

It works on basic science and laws of physics. Radiant cooling surface temperatures, and hence "output", is limited by the ambient dewpoint in the space it serves. Control the ambient humidity and lower the ambient dewpoint, and one can use lower radiant cooling surface temps and more "capacity" can be found. The issue is mainly one of designing the building to have very low cooling loads in the first place, to allow radiant cooling to work without approaching the dewpoint. Many climate zones of North America WILL require de-humidification to allow enough radiant cooling capacity, but in any event the de-humidification is required for healthy conditions anyway in hot/humid climates.

Here is an example of one recently completed project that uses radiant slab cooling and heating:

http://www.pmengineer.com/CDA/ArticleInformation/coverstory/BNPCoverStoryItem/0,2730,163495,00.html

Mike Lampkin_2

Radiant Ceiling Heating/Cooling

I would like to find out, if any contractors have tried out radiant ceiling (cooling/heating) in a residential home and how it has worked out. I'm very interested in learning more about it, especially what is the temperature of the water in the tubing is, when in the cooling mode? I know that de-humidification is very critical, to prevent condensation on the ceiling, so how is this typically handled? By using the radiant ceiling to do both heating and cooling, the size of the ductwork could be kept much smaller since it would only have to deal with the ventilation and humidity requirements.
Thanks
Mike Lampkin

Tony_23

water temps

Temps vary dependant upon dewpoint of the air in the room/house. That way the panel doesn't condensate. It won't dehumidify the bldg, but it will remove heat to a point.

I would suggest you check out www.healthyheating.com and post your questions there as well.

Gordy

Ranger

We had one customer of ours...

..install radiant heating/cooling in a sun room.I believe
the slab cannot get below 65F or it will sweat.There is a 12 hour "swing time" between heating & cooling.I believe in Europe thay are doing this w/desicant wheels and air
exchange but I do not know what there Sensable & Latent conditions are over there.
Ranger

Mike Lampkin_2

Congratulations Geoff....

That's a spectacular looking project that you completed.When working with radiant cooling, are dew point sensors ever used used? I was checking out Venmar's "DUO" air exchanger which limits the amount of humidity which comes into the building, thereby, reducing the load on the cooling system.
Regards,
Mike Lampkin

Rodney Summers

Humidity sensors

We're lucky enough to live in a climate zone where the outdoor ambient dewpoint seldom goes above 62F-63F and the design cooling temperature for the slab on the west facing zone is (drumroll)....63F to get about 25-28 Btuh/sf of cooling capacity. The trick is to design the building envelope so that the solar gain does not exceed the magic 25 btuh/sf cooling load "limit" of the radiant cooling system. We have humidity sensors scattered around the building to keep track of the RH in the rooms so if the room RH exceeds the 60% RH at 76F ambient air temp, then the slab system resets the fluid temp up a degree to ride above the dewpoint. One must always keep in mind that the wet bulb temperature is not the same as the dewpoint temperature.

The Fred Kaiser Building is now one of five radiant heating/cooling slab systems here on the "Wet Coast", so the small group of radiant cooling/radiant slab system specialists in my area are keeping tabs on them to allow us to expand our design database. The hardest part is getting the architects in line to get the good envelope and glass solar performance required. Lots of resistance due to ignorance of window properties and building physics.

Ranger

Geoff

Yes Sir,You are correct.I am sorry,I do not articilate well.

Mike Lampkin_2

Resetting the slab temp...

What type of controller did you use with the humidity sensors to reset the fluid temperature in the slab? Would a controller like this be practical for a residential project. Thanks

[Deleted User]

Numerous manufacturers...

will be introducing dew point cooling controllers int he near future. One of them is old line big name.

ME

Mike Lampkin_2

Thanks Mark and....

Congratulations for the article "The Consumers Guide to Purchasing Radiant Heating Systems", which you wrote for the "HealthyHeating" website. By the way, have you installed any radiant cooling systems as of yet? It sure looks like it's coming down the road. Regards.

GMcD

Controller

Basically we had a DDC computerized building automation system, and the two main slab "zones" (west offices, and east/interior/everywhere else) are served by a primary/secondary pump arrangement so each slab zone can be controlled to different slab water temps via the 3-way mixing valve at the secondary pumps. The "primary" slab water is controlled based on seasonal temperature: start out in January at 26C, Feb=25C, March=24C, April=21.5C, etc till May/June when the primary slab temp=16C, and stays at 16C till September when we start to rise again. There is also the ability to use room temperature sensors and outdoor temperature trends to reset the primary slab water temp up or down for small monthly variations. This function has been a problem during the first summer/fall season since the building was only half occupied and the majority of rooms were satisfied at an 18C slab temp, but, of course, a few occupied rooms were too warm, and as we are getting into the heating season, the slab temps were averaging about 22.5C, but the NE office guy was too cold (room temp=19C with ceiling at 22.5C) The quick solution is to disable the feedback reset function from the room sensors and fall back to the straight monthly primary slab water setpoint and wait till the building is fully occupied. The usual tweaking of the system and controls setpoints through the first year of operation. Even if this was a conventional HVAC system, the first year of operation still requires a certain amount of fooling around to get it set up for the combination of users and equipment. Hey, ASHRAE Standard says the best we can do is satisfy 80% of the people 80% of the time....

GMcD

No sweat

I find a lot of near "religious belief" from the conventional HVAC systems designers about radiant cooling- the knee-jerk reaction is: "it won't work, indoor rain, not enough capacity, etc." - basically dismissing it without doing the basic math and physics. Similar to the fervor with which "natural ventilation" is a mantra to many Architects - sounds warm and fuzzy, but do we really want to be using raw, unfiltered outdoor air in our buildings? And to make natural ventilation work, the building generally has to be under negative air pressure, a fact that gives the building envelope and moisture penetration crowd severe willies.

[Deleted User]

Your welcome...

and thank you for the kudos.

I have numerous potential projects for rad cooling, but none installed as of yet.

ME