Considering ceiling radiant in new construction

ddunn

I'm working with an architect on designing a custom house in the Seattle area.

The current leading candidate for heat on main level is radiant floor (aluminum plates under subfloor). But after doing some research, I'm thinking about proposing radiant ceilings instead.

Two reasons for considering ceilings over floors:
- main living area has floor to ceiling west facing glass (sliding wall) for view. I'm imagining we may go from needing heat, to not needing heat, then back to needing heat in pretty rapid succession. Combined with slow response, that may be unpleasant.
- I like plush carpet in private areas
- we are used to using setback and like the cooler setting at night

Living area (entry/living/dining/kitchen) has sloped ceiling rising from 8.5' to 10.5' towards west facing windows at roughly 1"/foot; hardwood floors. 8.5' ceilings in other areas; likely carpet.

My rough estimate is 15-20btu/hr*sqft at design (26F) in living area (over half the loss thru windows) and 10-15btu/hr*sqrt elsewhere in house. Seems high given my current therm usage; our poorly insulated home in same location used under 10btu/hr*sqft during an unusually cold Jan 2017. But we'll get accurate model-J later when we hire the ME.

Questions:
- heat lamps used on patios make me feel terrible when I'm anywhere near them, will radiant ceilings feel similar?
- will radiant ceilings sloping up towards glass wall create a convection loop of cold air blowing across the floor?
- other things I should consider about radiant ceilings?

The other option I've been considering is using a mini-split as backup heat in living area and limiting the floor temp range. Or locking out the floor when outdoor temps are moderate. Tekmar thermostats seem capable of handling those types of adjustments.

Any opinions?

Thanks,

Dave

Gordy

From what I see your setpoint patterns are, and flooring wants your assumptions for using radiant ceilings are correct.

It will not be the same feeling as a patio heater, or overhead infra red heaters. More of a mild feeling like being warmed by the sun.

You should not get noticeable convection streams.

As with any radiant heating system proper control strategies is a must for the most comfortable, and economic operation.

Mark Eatherton

Radiant in general is not conducive to set back. It causes discomfort due to over temp during recovery periods.

I'd suggest zoning sleeping areas separately from other common living areas if you like a cooler sleeping environment. Also, if you have any cooling needs, the radiant ceilings are very conducive to those needs. You will need to address the humidity (latent load) with a separate stand alone system, but you can handle the sensible cooling needs with the radiant ceilings for sure. I have radiant ceilings in one of my homes, and I LOVE them. I think it is one of the most overlooked opportunities there is for delivering excellent radiant comfort.

Gordy's assessments are correct. He too lives with a radiant ceiling system.

ME

ddunn

Gordy and Mike,

Thanks for the speedy input. What ceiling surface temps are you using at design?

Gordy

Depends on your design, and. Me 100 degree avg. water temp at design of -9. Yielded a surface temp of mid 80's.

However my usage was a single setpoint of 70 all winter. Set it, and forget it. If you were to set back as Mark pointed out with out proper control you may see higher surface temps coming out of a set back until the mrt reaches equilibrium.

ddunn

For adding cooling to a radiant ceiling, it seems like an air to water heat pump is required.
Any suggestions for decent air-to-water equipment in the 2-3 ton range?

It also seems like a mechanical engineer and contractor that has done this before is required.
Any suggestions for professionals in the Seattle area that have done radiant cooling in a residential setting?

Thanks

Ironman

MultiAqua and SpacePak both offer variable capacity, inverter air to water heat pumps. They both call it a chiller. They also offer hydronic fan coils that look like mini split units to go with their system.

Getting your system designed correctly is the most important step. Be very thorough in vetting your designer and contractor.

I believer @Paul Pollets is in your area. He's a good one.

jumper

Now that efficient dehumidifiers are available,ceiling radiant cooling can work very well. With low humidity higher air temperature is comfortable.

Gordy

It takes competent design to use radiant for cooling. As been said you will need to cover the humidity carefully to avoid condensation.

The radiant would cover the sensible load (cooling on the thermometer) and the latent would cover the (humidity) part of the load.

The latent cooling system ends up being considerably smaller in size, and distribution.

With that being said it takes prudent design experience for sizing the two systems. You must beable to control the dew point effectively.

jumper

Does he need distribution for latency control? A couple of free standing dehumidifiers should work. Water vapor diffuses quickly?

Gordy

Depends on region. Southwest maybe.

Gordy

Remember the op is in the Seattle area. They don't tan out there they rust . At least that is what my cousin claims.

ddunn

Thanks for the advice and recommendations. I'm going to pass this along to my architect this week.

Yeah, Seattle has high RH but fairly low dew point. 53F is average summer dew point (lower than Phoenix). Rare to go above 60F dew point. And 67F dew point is the record high.

I definitely want automatic humidity control to keep it safe, but the latent cooling load around here is pretty minimal. So is the overall cooling load if you don't have west facing views (glass).

Maybe a coil in the HRV is sufficient? We'll have to see what the designer ends up recommending.

Gordy

Personally I'm fine with higher ambient temps so long as the humidity is managed. 75 is comfortable. That's me though.

Mark Eatherton

I'd recommend hiring Robert Bean of www.healthyheating.com for your mechanical designs. Remember, the only truly effective way to avoid condensation production is a very tight home. Robert may know of a contractor that can help you. I think once you have a competent design, any contractor worth their salt will be able to handle the work.

ME