Thermaray Electric Radiant Ceiling Heating System?
Tiziano
| Posted in Energy Efficiency and Durability on
Anyone have experience using a Thermaray Electric Radiant Ceiling Heating System? The main company seems legit (https://thermaray.com/residential-radiant-ceiling-heaters/), but the nearest distributor to me has no address on their site (https://premierenergyusa.com/) so I’m leery.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
This is an old idea form the 1950s from a time when we thought electricity would be too cheap to meter.
This is pure resistance heat and will be very expensive to operate give todays cost per kWh.
If you install a heat pump instead your bills will be a quarter of what resistance costs to operate.
Walta
Thanks. We can get to -20F during some nights in Jan and Feb, so I'm not sure about heat pumps yet.
Tell me your county or zip code and I'll do an analysis for you.
55331
OK, the analysis I did is here:
https://docs.google.com/spreadsheets/d/14v7VA7I9W6ctAcoPxDZDnEAI4Xvi7JO0g4Rgbe-BHHU/edit?usp=sharing
The performance of a heat pump depends greatly on the location, the equipment and the house, so for the sake of an example I used a Mitsubish P-Series and assumed a house with a heating load of 40,000 BTU/hr. You can see the performance data for the heat pump I used at: https://ashp.neep.org/#!/product/34535/7/25000/95/7500/0///0
From the NEEP.org website I used performance data for that unit to estimate what happens to the output and efficiency as the temperature drops. That website also has climate history data, which I downloaded for your zip code to get the hours per year at each temperature.
According to the climate data from NEEP, the design temperature is -6F and the coldest it typically gets in a year is -24F. Based on those assumptions, that heat pump would meet 96% of the heating load, 4% would have to be provided by a backup heat source. If that backup heat source is resistance electric, the weighted seasonal coefficient of performance (COP) would be 2.4; ie, a pure resistance heating system would use 2.4 times as much electricity. It would use just over 11,500 kWh per year for heating.
The heat pump meets 100% of the heating load at temperatures above -8F. I assumed zero contribution below -13F. There are so few hours below -13F that changing the assumption to some heat pump output changes the annual electricity by less than 100 kWh.
Assuming only backup heat below -13F, it needs to be able to meet the full load at -24F, or 51,000 BTU/hr. That's about 15000 Watts or about 60 Amps.
Thanks. That's pretty cool.
Given the size of the structure (12' x 16' with a mono-slope ceiling 13' high down to 8'), and 54 sq feet of windows on the north wall, I'm not yet sure what BTU to plan for.
Maybe this: https://gotductless.com/products/msz-fs06na-muz-fs06na-mitsubishi-6-000-btu-hyper-heating-single-zone-system
What's more important than the size of the building is the insulation level. If you tell us your insulation in the roof and walls we can estimate the heating load.
My Rheem heat pump heats my house down to +6°F with the strip heat locked out.
I do not feel bad about using the strip heat for the few hours each year they are needed.
There are vapor injected heat pumps that run well at -15°F.
Walta
Thanks!
Tiziano,
I grew up with ceiling radiant panels in one part of the house. The pitch for them was from good ol' Reddy-Kilo-Watt that indeed pushed a future of nuclear power too cheap to meter. Needless to say that part didn't go too well.
Of more interest to you might be the rather poor performance and the mounting problems encountered. The panels were thick and the wiring needs forced us to redo the entire ceiling as well as the electrical panel. Still ugly once done. After activation it became pretty obvious that a standard 8' ceiling left one's head too close and feet too far to be comfortable. New panels may have altered the heat signature compared to the ones I knew, but two things became very clear.
First, the heat pattern from above created a fairly sharp gradient of warm tops and no warmth under tables or desks. (a home office was the original driver of the remodel) This might have been less noticeable in a highly insulated home, but we are talking the 60's. The second thing meant I did enjoy the ceiling location. My reading getaway in the attic was veeeery warm all winter. The panel's heat output seemed to be equal up and down.
As an alternative, I would suggest what I am using now for my entire heating, radiant cove heaters. (Link at bottom, no reward to me) These seem to project the heat as very long wave infrared which has proven quite even and capable of carrying our heat needs which seem similar to yours. We have about 7800HDD and several nights a year that go to -10F or lower. The cove heaters high on wall location means we have freedom of furniture placement and no pet hair to remove like baseboard or the wall panel types. And little hands can't touch them. Visually, they are less obtrusive than wall cassettes for ASHPs and dead silent.
DC has correctly noted the very KWH hungry nature of radiant, but you are only seeking supplemental heating when the ASHP is at its lowest COP. Of course if the ASHP craps out or freezes over than at least you have survival heat. Allowing for panel space will be your biggest concern if mixing the two heat sources with all electric appliances. Separate thermostats would limit their activity as needed.
I fully support the new ASHP tech that provides decent COP levels down to zero and beyond and would have gone a mixed route IF I hadn't been building before such units existed. I am also at a high enough altitude that de-rating of all traditional appliances factored into my final choices. More notes on how things are 10 years on, if you like.
https://www.radiantsystemsinc.com/
Thanks for that report. I hadn't thought about the problem of feet hiding from the heat under a desk or table. Compared to a radiant floor, a radiant ceiling is great if you are lying on the couch but not so great if you are sitting at a table.
Floor R-39
Walls R-35 (assuming I can find Huber ZIP R-12 in my area)
Roof R-60
Tiziano,
I see that you are likely on a lake not far from a relative of mine. The temperature swings are something there.
Your entire interior surfaces only add up to 900 sq ft plus another 72 sq ft for windows and doors. With an average of R in the mid to hi 30's you should have surface losses of ~2455 btu/hr at minus 20 assuming 70F interior. Windows and door add ~1080 btu/hr if R-6 rated.
Add in the air exchange losses and round up to worst case of ~4200 btu/hr and more typically 3000 in the winter. Of course you have the joy of 96F summers to deal with, but you originally asked for ceiling heaters. I still stand by the cove heaters over other choices. You would need very few depending on how you divide the space. The advantage I have found is the long infrared heats objects and not the air, (at least not directly). With the high pitched ceiling you will need to have some sort of fan to break up the stratification. Other wise any loft space would be over heated.
If you can get the R-12 ZIP, I would suggest considering let in bracing as a back up anti-racking feature. Lake winds can be fierce and the fastener requirements for the R-12 are very particular. The long nails needed can be an issue as well as making sure the crew does the pattern carefully.
I'm evaluating all heating options that are electric. I'd prefer gas, but don't want to run a line from the house. Radiant panels was something another forum led me to and I'd not heard of them before.
After the good information from all in this thread I'm leaning towards a small mini-split and a baseboard hydronic backup on the floor of the tall wall. Plus a small ERV/HRV system.
I'm the one and only crew member, plus family and neighbors for heaving lifting.
Looks good. Are you going to have overhangs? Particularly with that high wall you really want to keep the rain off of the side.
I updated the spreadsheet to show a 1.5 ton Mitsubishi HyperHeat, https://ashp.neep.org/#!/product/67809/7/25000/95/7500/0///0
According to FERC the average residential electric rate in MN is $0.16/kWh. With full resistance you'd pay a little of $1100 per year for heating. With the heat pump it would be $450 per year.
Thanks for the updated sheet!
As for overhangs, I'm in a bit of a bind. To limit the depth of the overhangs I decided to eliminate the rafter tails and add overhangs coming off the 3 layers of rigid insulation. Of course I'd need to frame that out somehow.
Ideally I'd add 12" overhangs to the rake sides.
On the south end I'll likely make the overhang much longer and use some kind of angled support (corbels?).
The north end (high wall) is a problem because I'm trying to get as much light as possible into the building from the sky. One thought I had was to add a short overhang roof (12"?) to a 2x10 that's acting as blocking on the end of the rafters (not shown in the images I added earlier). That 2x10 would then also be a ledger beneath the ZIP. The short roof would pitch down (opposite the direction of the roof) and direct water away from the wall. 12" is not a lot, I know, but maybe it's enough?
DC and Tiziano,
To be clear and loud, I am not against heat pumps! As I have noted many times before on other threads, I would have put one in but for the lack of appropriate technology when I was building. Where I live, the AC value of heat pumps is moot, thanks to the diurnal temperature swings. My house design is also not heat pump friendly like some open floor plans. In any case I am heating 2700 sq. ft plus a basement for $2400/yr. The HDD here is about 7800. You might guess why I was stunned at the projected cost of $1100 for pure resistance and $450 for a heat pump.
Your (Tiziano's) total surface area of walls, floor and ceiling only comes up to ~900 sq. ft. Windows and a door add 72 sq.ft. of much lower R value surface. Provided the R levels proposed are met, I would think that body heat alone will carry you into the fall. Assuming a median R-34 for framed surfaces and R-5 for door and windows, I am seeing (at -20F) an ~4346 btu/hr loss for all surfaces, windows and door included. That would be 1.275kWH/hr or 30.6KwH per day of -20F. That would be about $4.90 a day for pure electric resistance heat at $0.16/kWH. $1100 of energy translates into 224.5 DAYS of minus 20F weather. I admit MN is extreme, but I am pretty sure not that extreme.
It looks like you are planning a nice studio space away from distraction. Painting if I am interpreting the high north windows correctly. No kitchen, toilet or other confounding details. I think that a case could be made for skipping the expense and aggravation of an oversized heat pump unit in this very special case. A window AC unit could easily carry this space during the notoriously muggy and hot MN summers without worrying about drain lines from head units and other maintenance issues. Current window AC units are quite efficient. I feel the payback period on the much higher front end cost of a heat pump in this case makes the KISS principle a winner.
The cost of two 1500W cove heaters will set you back about $700, another $100 for quality thermostats. They mount high and won't interfere with furniture or flat files like baseboard heaters. I don't know the amp demands of the heat pump unit suggested, but I imagine that it will take some very heavy gauge wire to make it out to the studio either way. Can the current panel handle the added load? The heat pump will likely be short cycling a lot of the year given the tiny loads you seem to present. I would definitely get a quote for a heat pump before getting married to the idea. Remember you live in a snow region and the HP wil need protection or clearing and the COP falls with temperature except for the most sophisticated units. Minus 20 is a tough range to operate in.
Additional reading: https://www.greenbuildingadvisor.com/article/frost-on-heat-pump-outdoor-units
https://www.greenbuildingadvisor.com/question/ductless-mini-split-condensate-drain
Side note: Gas would likely be a no-go if you planned on tapping into the current house feed. The distance and cubic foot demands would probably exceed available volume and pressure capacity.
Thanks onslow. Great info in your posts. I appreciate it. I'm still unfamiliar with some of the terms, so I'm likely not as responsive as I ought to be.
In fact it's only now that I looked up Cove heaters. I had assumed the word was a generic term and so I skipped past it. Anyway, it seems to be a far better option than the Thermaray. You make a good case for rethinking the heat pump, especially given the small size of the structure relative to the cost of the unit.
I'll need to study the window AC idea some more. At present I've no window available for it, but maybe framing in an opening for a unit would be fine. I'm ignorant enough about them that I simply skip over the idea due to the assumed heat loss through it during the winter. But I suppose one would remove it when it's cold outside.
Yep. My house is underpowered as it is, so my neighbor (who owns a commercial electrical co) and I are visiting my options.
There are through-wall heat pump units, you see them a lot in motels. For a building your size that would be a good recommendation.
The problem is in your climate you really need a cold-climate heat pump, one with vapor injection ("HyperHeat" or similar). And those have limited choices for both capacity and form factor.
I've looked into PTACs a bit and am not yet sold. My experience is limited to hotels and in every case I've noticed stains on the floors (leaks from the units). Plus, noisy fans.
But, maybe that was all old-school units.
Onslow,
I contacted Radiant Systems and they suggested 2, C12024 heaters.
Since I’ve never been in a room with this kind of heating, can you describe what it feels like?
In other words, does it feel like hot water radiators?
My wife is sun-sensitive. During a walk yesterday I tried to pay attention to how the sun feels. There is a definite felt ‘force’ from direct sunlight. Is it like that?
Or is there no feeling at all?
I assume the room maintains it’s temp even when no one is present.
Thanks.
Tiziano,
Your wife should be just fine. If you are under four feet from the face of the cove you can just feel a very mild warm. Even inches away it is not much more than heat from the side of a toaster. I am bald on top, so maybe I can feel it better than most. Mostly they are invisible to the senses. They just operate in the background and life is quiet the way I wanted after too many years with noisy furnaces. And trouble free for over nine years now.
Unlike with traditional forced air furnace output, the room air stays very close to the set temperature. The wall directly behind the heater will get warm and if placed just below the ceiling as shown on the web site, the ceiling will warm as well. I will take some readings with my infrared thermometer once mine kick in for the season. So far we are staying above 70F mostly on appliances and body heat.
I would recommend the two be placed on opposite walls mid way between the high and low ends about 9' (or bit less up) from the floor. A small ceiling fan set closer to the high windows will help stir things and keep the window glass from becoming too cold. The size recommendation is good. Each 1200W equates to ~4100BTU output per hour runtime. Having two on opposite walls will reduce the gradient you might see across the room and keep the run times within the limits set by the thermostats. At least the Honeywell ones I used. I will see if I can find the correct model number, as it is less expensive to get them independently. An interesting feature of them is the ability to run the coves at less than full bore.
I have found that with sufficient insulation, like you have proposed, the run time is quite low most of the winter. My similar levels of insulation mean that only one unit has come on so far and we are down to the low 30's at night. Next week we will not see highs above mid 30's, so I expect more will kick in. Thermostat placement is important, as you can't have them facing the cove heater. The pattern of heat projection is somewhat like a LED shop light. The spread is not like a round bulb. This is helpful for putting the heat where needed. The brackets supplied aim downward at an angle suited for 9 and 8 foot ceilings. I do tend to notice the upstairs ones a bit more than the downstairs ones. Mostly because I stand closer to the one over my dresser.
Hope you can figure out a way to run power the distance without giant gauge wire. Keeping all the lighting LED will help. By the way my heat load calculations included a bit of losses for air exchange. I didn't point that out the first time. Don't skimp on the windows or you losses could go up dramatically. Though mostly that is for temps under zero. You will have to judge the local weather trends. And, you can't paint them. Order a color if you want color. Painting will mess up the function according to the company.
Thanks onslow.
So about +/- 9' from the floor. I assume the gable walls (if they can be called that in the mono-slop design) - meaning, the walls that are 13' on one end and 8' on the other.
Speaking of insulation... I'll start another thread about storm windows, etc. because most of the windows in the tall wall will be blocked during the day. And, at night, there's no need to have any unblocked.