Passive Solar and Radiant heat

Unknown

I think free heat is better than not free heat. but what *really* needs to be addressed is not my thought, it's the client's expectation. If they want a solid 70 degree room temp 24/7, then sure, lower those blinds (or open a window, it's free heat).

However, they might be happy to be a little warm in the morning if they realize it's that much more energy they won't have to burn later.

This could be less of a problem using nighttime or scheduled setback, properly positioning your outdoor sensor, and using indoor feedback as well. Or slab sensing and using low mass radiant ceiling for fine tune heating control.
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Kevin_in_Denver

passive, radiant, and high mass systems

have created a lot of controversy here. Siggy himself has worried about the combination. See his column

http://www.pmmag.com/pm/cda/articleinformation/features/bnp__features__item/0,,4148,00+en-uss_01dbc.html

Setpoint overshoot is the main concern.

I'm building a house like this, but I'm not really worried. My bathrooms may get cranked up in the morning, but they are all on the north side of the house by design.
I think the problems have arisen from customers who expect constant temperature. Unless you have a huge thermal mass, passive homes should be expected to reach the high 70's on a sunny day.

One of the unbreakable laws of passive is that you need thermal mass, period. The more the better, up to and including enough to get through the whole winter without backup. (Google PAHS or passive annual heat storage)

One of the things I'll be checking is if constant circulation will effectively make the house "isothermal".

A great website dedicated to a passive radiant house in www.ourcoolhouse.com . Phil hasn't mentioned this problem, but I'll quiz him.

Mark Eatherton1

The problem....

lies in the lack of a control device that can differentiate between a cloudy night sky (no imminent solar gain potential) and a clear night sky (imminent solar gain probable, and night sky re-radiation occuring). When and if someone comes out with this simple digital interface, your south facing zones will now when to ignore a call for heat during the early morning hours, and when to pump heat to the calling zone.

For the mean time, it will require you to be the intelligent interface between your hydronic heating system and your passive heating system. When the logic becomes available (hopefully in the next 5 years) it should be an easy interface.

Trust me, I've studied the night time re-radiation sensor potential to oblivion, and it is feasable...

Just a matter of time.

ME

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GMcD

Solar control

My take on the "problem" is lack of solar control. Passive solar relies on an "average" of solar exposure and is subject to the randomness of nature. A good slab sensor with some good anticipator and PWM algorithms along with some positive exterior shading control (manual or automatic) to allow "just enough" solar when the sun is available ought to temper or eliminate this "problem". Most passive solar houses tend to have very little adjustable exterior shading- usually it's fixed to keep out he spring/summer/fall higher solar azimuths, but configured to allow the low winter sun in when you want the passive solar heat. Interior blinds/shades are "some" use, but once that solar gets through the glass, it just heats up the blind which is inside the house. The warm blind acts as a radiant heating panel. An exterior adjustable blind is what is needed. Keep the solar controlled outside the glass. I see the hydronic radiant slab as the primary heating system and the passive solar as "bonus" secondary heating when it's available.

Bob Gagnon plumbing and heating

I simply

zone the south facing rooms seperately if they have a lot of glass. with a low-mass radiant system this works great. when the sun comes up, the room thermostat is satisified, and with a low mass system, it dosen't overshoot like slab heating. when you need more heat at night because of all the windows, the south-facing zones will stay on longer. the room temperatures stay constant in the north and south sides of the house. it is a simple solution if you have a low-mass system. bob

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Kevin_in_Denver

Weather Predicting and Heat modulation

Every night, the TV tells us what temperature it will be tomorrow. Are there any controls that can take that into account?

I personally wouldn't mind plugging in that number every night. As it is, I'll be making some sort of decision like that every night, such as opening the windows or not, or closing some window insulation.

Larry Weingarten

South?

The way we are trying to get around temperature swings in the house we're building is to face it North. I know this sounds heretical for a solar house. On the South roof are solar thermal panels which will put heat in a large solar tank in the basement. So, we get the high mass.. and the ability to move it around as and where its needed. It is a SIPS house with panels on all six sides, so heat loss is minimal to begin with.

Kevin_in_Denver

Back up heat?

But, you probably still have $8k invested in your fossil fuel backup system, yes?

Larry Weingarten

Well, no.

Actually I only needed to put a heat exchanger on the water heater to back up the radiant. The distribution side is all gravity driven. Heat loss is low enough, that's all it called for. Really :~)

PJO_5

Of Blinds and \"Controls\"...

When we built our house six years ago, I purposely oriented it for the sun...and have been dealing with these situations for six years now.

I have a "medium mass" system as far as things go I guess; staple up with plates under 3/4" subfloor and 3/4" oak finished floors in two zones downstairs, three bay garage slab 5" inches thick, and baseboard upstairs. I do have a lot of volume in my system due to an Ergomax in the primary for my radiant, which was a story in itself because of some idiot buying non-barrier tubing seven years ago (yes, that idiot is me!).

I welcome the sun in most of the time, and do the "anticipating" myself with programmable t-stats...management just shakes her head at me :-)

To avoid gain when needed, I have found that wooden white blinds work pretty well - and don't heat up very much either. For the double full glass doors on the south side, a full curtain (above top of door and touching the floor) with insulation and a white exterior side is excellent...great insulation at night and doesn't pick up heat when we don't want the passive solar. Now if I can figure an anticipator for curtains to close on those clear nights in the winter by itself...

The Europeans apparently use the exterior blinds a lot in these types of houses from what I've read, but they are pretty expensive and management doesn't like the look.

When I get a differential of more than four or five degrees from passive solar between the front and back of the house, I put my air handler on for about 15 minutes and this evens things out pretty well...one zone on each floor...but it bugs me that I'm now using electricity to move my solar heat gain. I was thinking of piping in two solar pumps to slowly move the warmth through the floors (primary/secondary system) but then my feeble brain starts to short out on how to do it...zone valves, convection still there that's still not sent to the front, etc.

Yes Geoff, I agree that the radiant/baseboard heating is the primary and the passive is the bonus...free and clean.

Take care, PJO

Mike T., Swampeast MO

One of my Goofy Ideas...

"the lack of a control device that can differentiate between a cloudy night sky (no imminent solar gain potential) and a clear night sky (imminent solar gain probable, and night sky re-radiation occuring)"

Unless the house is a virtual thermos bottle with utterly phenomenal insulation and virtually zero heat loss, there is such a control and it's even built into the system! The slab itself!

Think about it. If the nighttime sky is clear and you're getting re-radiation, the slab is going to be loosing temperature more rapidly then if the nighttime sky is cloudy (given the same outside temp of course).

It will require extremely sensitive temperature measuring devices and "learning-type" logic, but I believe it could be done fairly easily and amazingly accurately.