solar gain and heated floors

jerry scharf_3

Ken,

IMO, the only way to solve this is to damp the zone before the heat gain occurs. This is way beyond what commercial controllers can do, both because of complexity, stability and lack of necessary information.

Once you're in catch up mode, the next best thing is to circulate the air to other rooms. This has limited effect, as the MRT is still high, but both the air motion and the lower air temp do help the comfort. This assumes you have some form of central air system and dampers/actuators that can be operated by the control system.

Finally, you can reduce the heat coming in. That kind of defeats the purpose of having the windows in the first place. But it beats cooking.

There are a couple things you can do if the system is in design. One is to use as low a radiant mass as possible, like hot rod mentioned. Another is to only provide part of the heat with radiant, and use panel rads with TRVs to cover the rest. It won't have the negative temperature bias, but it would probably make the most comfortable system available for a sun room.

jerry

Ken_25

Solar gain with heated floors

When building a house with southern exposed windows, which will allow much winter sunshine; how do you best set up your radiant floor or controls to reduce overheating?

I understand how more pipe in the floor keeps your water temperatures lower, but you are still putting out as many BTUs overall. How does lower water temperature benefit the overshooting caused by the solar gain?

How do floor sensors fit in this picture?

Thanks
Ken

Ken_8

PS. That's not me posting above...

Different "Ken"

Perhaps the poster above could be 8-Ball Ken? Side pocket Ken? Or Ken 'O'?



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Wayco Wayne_2

Tekmar controls

Some of the Tekmar controls have an indoor sensor that shifts the outdoor reset curve when there are internal or solar gains that lower the normal need for heat. The Buderus logomatic control also has an optional indoor sensor to reset the outdoor reset curve. I've used both with rooms with large solar gain with great success. WW

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Andrew Hagen (ALH)

Reset

Do you have an outdoor reset control?

That would be my first line of attack. Keep the fluid temperature as low as possible.

-Andrew

hr

That old \"ball of fire\"

will trump any control logic you can throw money at Any stat with an air and floor sensor will give you about the best control possible. Tekmar and Wirsbo have one of the best. But in the end, you still need to be able to manage the solar gain.

Ideally automatic shading would be sweet. At least some manual operated blinds to get a handle on that powerful solar gain.

Others might suggest low mass panel radiators in lieu of a high mass slab. But if you want warm floors, and to minimize that overshoot, perhaps a light "on top" radiant floor might be better. WarmBoard, QuikTrac, etc.

hot rod

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Doug Wagoner

Winter time solar gain on radiant floors

I live in NC and have the same problem. But I have AC and the duct work for this overlaps my radiant southern-exposed bed room and a northern-exposed living room. When the day is going to be a big solar day I switch on the air handler and let the air move the excess heat to the cooler room. Easy to do on new construction but more difficult where there are no AC ducts or no zone overlap. The days I forget I have a solarium--hot and dry-- 85 degrees. When I do not forget--a comfortable dry 75 degrees. The radiant floor controller is set at 69 degrees and constant circulation.

hr

Think about it

that floor becomes and indoor solar collector. You could move excessive energy hydronically, also. With some 3 way zone valves you could use a floor sensor to divert that energy SOMEWHERE else.

BUT, the delta t may be low from the "collector" slab to the back room slab that you are trying to dump to. Perhaps dump it into some insulated storage tanks for use later when needed.

It comes down to how much money, and technology you want to throw at storing, and moving a low grade "free" energy around your building

hot rod

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Mike T., Swampeast MO

Passive Solar

The best designs I've seen incorporate:

1) A way to limit both solar gain and nighttime loss. As Hotrod mentioned, automatic window coverings are best. Manual works fine if you're diligent.

2) A way to move some excess heat before you have to resort to blocking the sun via shading. Probably the best way involves the structure as a whole--you design for natural convection so that warm rising air is given a way deep into the structure with cool "return" air from the rest of the structure entering low in the solar space. Sometimes fans assist the air movement. Have heard of (but neither seen nor felt) hydronic systems that "move" the excess gain. As mentioned, while there might be a lot of energy available, it's quite low-level and thus difficult to utilize.

If there is not an intention to use passive solar, then Hotrod again gave a reasonable solution if you still want warm floors--use something like Warmboard which has little mass but high heat transfer ability.

J.C.A._3

Just thinking out loud here....

How about installing a simple Honeywell T-87 as an air sensor that would interupt the floor/slab sensor circut, shutting down the pump?

Maybe I'm thinking too simply, but it seems that if the air temp. is too high from solar gain it should take over for the slab/floor sensor, at least for a while as the sun passes overhead. As it goes by, the circut will close and let the slab/floor sensor take control again.

Too simple? Chris

Ken_25

It appears the reason I hadn't been able to grasp the solution is that there isn't an easy one. It does seem a waste to block out both the free solar heat and the view as a solution. I think I will investigate the idea of moving the warm air elsewhere.

I had a rental unit at one time which had a wood burner upstairs. the tennants would get too hot and then open the windows. the cold air coming in would go down the stairs and make the basement colder. I put a hole and a fan in the living room floor to blow the upper air down to heat the basement. this only made it worse when they opened the windows upstairs.

I then put a kitchen counter height box over the fan hole to draw the warm air from that height downstairs. I placed a ducting under the hole to bring the warm air down to the floor level in the basement. The results were incredible. Both levels became much more comfortable.

It sounds like the same basic principles may still be the best solution. I just have to decide where in the basement would be the best place to exhaust this air without screwing up the comfort balance down there.

Thank you all for the help

Okanagan Ken

Unknown

I beg to differ hot rod. Indoor feedback is powerful stuff. Provided you have been maintaining a low-temp nearly constant operation system already (which you are, if you have indoor feedback), the slab can back down pretty quick.

I haven't yet heard of a problem with a system using outdoor reset and indoor feedback together.

J.C.A._3

OOOPS,

Missed the moving the air part.

Now I'm thinking a heat/cool t-stat where the high side kicks on a fan to move the warm air away from the space.

Again, maybe too simple, but just thinking an air sensor is the way. Chris

hr

I agree, Rob

but no reset device I know of can REMOVE heat that large solar gains present!

Lets just say the room is at 70 degrees at 9 o clock am. The reset, or constant circ system has the supply pumping 70 water to the slab. The heating system is basically off, no heat is being added to the space.

Now the sun shines into that space and starts the overheating process. i have seen sunspaces in the Mountains of Utah hit high 80's in the dead of winter without any heat sourse what so ever!

Either you attempt to limit that gain as it hits, or look for a place to dump it.

Possibly you could move it to other rooms providing you have rooms below 70, or whatever, that could handle the additional BTUs. Ideally in a comfortable living space you wouldn't have rooms at 60° that would be ready and willing to accept this solar gain. maybe overheat the basement for a while or let the hot air eascape through combustion air inlets

Of course,it is easier to move energy around with water (hydronically) than forcing air around. As we all know water moves 3500 more time the energy than air. Not to mention the parasitic lose involved shoving air around compared to water, probably the difference between a 1/12 hp circ or a 1/3 hp blower motor.

And still, instead of dumping it ANYWHERE other than where it can add in a helpful manner, store it in water, not in warm air at the ceiling in some other room. Seeing as the ceiling is generally the highest loss other than windows, when you drive such a high delta t ( stratified hot air)up there, 90° air looking at perhaps 30° outside temperature.

Plenty of ways to skin this cat, this is not a new or unique problem. Wasn't all that long ago solar groupies would pump warm air into a bed of rocks! Now there is some Flintstone Engineering if ever there was some

Design to embrace solar energy, not wrestle with it.

hot rod



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Mike T., Swampeast MO

Air

Hard to do it with air alone. Air is a lagging indicator of excess heat--the sun has heated the objects before the objects heat the air.

It can also be VERY difficult and extremely expensive to develop an automatic control system that can understand what the sun has and is doing. Impossible to develop one that fully understands what the sun will do.

Do you happen to have a high, sloped ceiling in the sun space?

Unless you design the sunspace as in integral part of the structure-wide conditioning system, you'll likely find it more economical (and comfortable) to block and/or discard excessive gain while preventing excessive loss. "Just" this is not particularly easy to automate...

Ken_25

I have built my house and have the problem with over heating the house in the winter mornings. It is lovely to have the sun start our day at the breakfast table and the beautiful view puts you in a good mood. To have to shut out the sun to keep from overheating is discouraging.

Now my neighbor is building with the house layout very similiar and he is planning on radiant as well. I was hoping to be able to give him a heads up on the "best" method to handle it. The local supply firms seem to use an of the shelf, one size fits all approach to their designs. It would be nice if he could deal with it better than my house does.

jerry scharf_3

The thermostat would do that already

Chris,

The problem is the stored heat in the floor continues to radiate after the thermostat has decided it's hot enough. By the time the solar gain becomes noticable, it's already too late. You could say that you're cooked.

jerry

jerry scharf_3

I resemble that remark

Mike,

It's tricky but not impossible. If you have any kind of solar energy collector, you have your "what's the sun doing now" information. That plus an understanding of the solar track, windows and obstructions gets you to a good first order. It also helps if you are measuring MRT rather than air temp to start with.

If you want to be a bit fancier, there are things called Terminal Area Forcasts put out by the weather service for pilots. It gives predicted cloud cover mong other things for the next 24 hours. So you suck that in to see if there are dramatic changes coming in the next couple hours.

None of this is "off the shelf."

jerry

Weezbo

this is an especially favorite topic ,now, i'd like you to ...

consider long rays of the sun in 30 below zero ....yes... you can have basically free cooling with little to no efforting .trick though is ,utilization of the heat ...storage would be good....let me layout an entirely different stradgey..it is one of Designe, ...of the Building.imagine if you will a dimension....where the rooms to the home faced in ward to a room covered with a glass roof.....what do you feel the outcome of such a building plan would have on the cost of heating the same sized building without the inner glass covered courtyard? how about this idea,? or ok similar idea glass picking off the free solar gain on this side and pipes going to the shaded side bathing the cooler side with heated air and able to open the panels of glass to dial out excessive gains ?these two thoughts seem to work in really cold climates...to me that passive solar designe such as that works...makes me think that building designes need to incorperate a Zone that Runs off the sun....and as it is technically an Outside wall( all 4 walls) there is the slowing of the escape of btus during winter and it is suprising the positive feeling that is given off from the space... it is trapped light it cant get away....i think a pool of water is warmer in the thin parts of the pool so, a thick "pool" of cement would kinda work the same way....cirulate the "Thin" parts of the cement pools hydronic piping into the "depths" of the cement pool and store the heat there...justa couple of way out thoughts... *~/:)

DanHolohan

More input

This is in the Library, along with a lot of other good stuff.

Solar gain and radiant

It pays to wander off the Wall.

Dave Yates (PAH)

Another solution

We install the outdoor sensor where it can "see" the first hint of sun. That way, it gets its own bit of solar gain before the home's solar gain gets too large.

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Ken_25

Off the Wall comments

Thanks, Dan, I'll study that this evening.

Ken