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We are just starting to plan an energy efficient home in sunny Calgary Alberta.  3500 ft elevation, south facing sloped lot with an excellent uninterrupted solar window.  The house is 29 feet wide and 60 feet long that runs lengthwise north/ south on the lot, 2 stories with a walkout basement and an underground carpark below the basement.  Logix asymmetric XRV ICF (claimed R28) construction top to bottom, Hambro floor joists with 4” cement floor for the basement, 1^st and second level floors. Minimum North glazing, maximum South glazing, calculated overhangs to reduce summer solar gain.  Proposed fossil fueled heat (Radiant in-floor) is NG mod/con boiler and indirect tank with solar assist for DHW. 

Yes, I need to use the design services of a radiant pro but I like to know a bit before embarking on any project.

 

Here are the questions: 

1) Can I effectively combine a Passive Solar House design with a high mass low temp radiant in floor heating system?  I am dead sure the answer is yes but I am unsure of how to do this effectively, particularly with PEX layout patterns and in the logic department. 

 

2) Can I effectively override the radiant heat logic and move the heat from the hot floor sections (hot from solar gain) to the cooler Northern floor sections with out huge air temperature overshoots?  Yes, we are prepared to live with some temperature overshoots. 

Any help or comments greatly appreciated.

Chris

ahh, I'll be interested in this, I have the same situation.

this is always tricky because the mass effect is hard to model as far as its impact on heat loads, and all that south facing glass is massive heat sink at night and/or during non-sunny periods, and we still have to keep you warm. So usually this means treating the main gain areas as major loads, which may drive up your water temperature requirements... sometimes.

We are designing a system like this right now using Oventrop "unibox" controllers which are flow-control thermostats, basically.. kind of like TRVs but for radiant... but with a "bypass" on them so they never truly close. the idea is to keep some flow moving even when the system is "satisfied".

however, this is admittedly experimental. I know a few people have attempted various constant circulation strategies but it can be otherwise tricky in multizone homes. If you are ok with "analog dial" control though, I think it's pretty elegant. Basic reset on the constant circ system and those boxes in each zone and you get true constant circulation without any wild overshoots (prior to passive solar factoring in). Now the question is... how much does constant circ really redistribute passive solar? That's the experimental part. It should help, but it's hard to say how much.

high mass and passive solar means temperature overshoot though, no way around that. the warmer you get during the day though, the more free heat you collected, so bask in it :D

One thing you could try to work into the design is having some mass that is thermally broken from the solar gain area. During the day you temper the areas that get solar gain by moving the heat to this area. During cooling periods you move it back.

There are examples of homes that have thermal chimneys in the center of the house made of concrete. They use fans to move hot air through these chimneys storing the heat during the day and releasiing at night. You can add to this a way to vent the chimney during the summer nights and use it for cooling as well.

I have seen examples of a square completely insulated chimney and I have also seen examples of where a double wall runs down the north- south axis of the home and has fans that move the air through the center.

The key here is not having the radiant thermally connected to this mass. The radiant only heats the floors and not this wall. This wall then tempers the whole system.

A staircase or elevator shaft with doors that break it thermally could be a design element that would work well as a thermal chimney.

Rob, I get you. In terms of the south windows, our architect and I want to work with insulated window coverings such as the Hunter Douglas Duette G1 triple cell blind. Not huge R-values (4.8 advertised) but enough to help counter the heat sink effect and hopefully lower the night time water temperature requirement. The action of these window coverings is motorized and will be controlled by some sort of logic. Thus adding more variables/complexity to the system.

So what you are suggesting with the Oventrop thermostats is a “smoothing out” of the heat/cool cycle where the extra solar gain energy is distributed through the rest of the mass via the bypass flow allowed by this thermostat? With the qualifier: “how much does constant circ really redistribute passive solar?”.

jmgill, what you are suggesting is transferring the energy using air and storing it in another thermal mass product such as a thermal chimney? I am assuming this chimney vents out side of the building envelope so HRV would have to be able to keep up with this design yes?

The more I think about this the more my brain finds variables. I guess if we get right down it, the problem is… we have a boiler working away at night to keep the whole house (whole thermal mass) up to temperature then,.. the sun comes out during the day and starts adding energy to an already heated thermal mass. Heck, I guess I could always keep the radiant heat thermostat in the sun affected rooms “off” and let the passive design do its thing and live with the overshoots…

Oih, this is going to be an interesting project. Thanks for the input!!

Chris

"The more I think about this the more my brain finds variables. I guess if we get right down it, the problem is… we have a boiler working away at night to keep the whole house (whole thermal mass) up to temperature then,.. the sun comes out during the day and starts adding energy to an already heated thermal mass. Heck, I guess I could always keep the radiant heat thermostat in the sun affected rooms “off” and let the passive design do its thing and live with the overshoots…" That is the problem with radiant and passive solar. You need those floors to be cool before the sun comes up. I like my warm radiant floors in the am, so I need another mass to store heat. The only time the solar chimney would vent to the outside would be in the summer and in our house the HRV would already be having to work harder because of open windows. I am sure there could be a work around with vents that open and close.

OK,
so here is a solution that I have used with Russian wood stoves. We have placed a coil in the upper portion of the stove above the fire box, these stoves get hot and will hold and radiate heat for some time12 hrs +.
So the concept is as follows. the loop to the wood stove has a pump and sensor ( Johnson Controls A419 ) any time the sensor is above X the pump is turned on and hot water sent back to the low temperature loop as an injector, the potential for over shoot is minimized by the fact that it mixes pretty quickly with return water. Now when a pump zone calls for heat it will utilize the available heat from the wood heat coil first before triggering a demand from the boiler. once the heat from the wood stove has expired the Johnson turns off the pump, boiler kicks in. This was applied to a 6,500 sq ft home, so I was able to reach the corners of the home the wood heat could not.
This would work with the solar slab as well.
Perhaps a 2 pipe system, pipe A would be the johnson control pump, always presenting solar gain heat to the secondary pump manifold any time the slab sensor was above X, pipe B would be used for supplying heat as needed, the only reason to do it this way is the switching of the system is simplified.
But there are certainly a lot of other ways to make a system work, I like pumps for there simplicity.
Dan

It's my experience, in designing a solar thermal system for my own house, that the first 80% of the benefit is relatively easy to obtain, and that the last 20% comes with a level of complexity that would make such a system impossible to maintain. I'd say, in fact, that it's neither green nor friendly to design a system that the next owner won't be able to maintain. Be careful!

Jeff

Dan, I like the idea of two pipes in the gain effected floors. This would allow some "shuffling" of the energy and add flexibility to the overall design with little cost. Even if it doesn't work that well it does not lock us in to one design model.

Jeff, I have to agree, the system has to be relatively fool proof (once tuned). "Elegance of simplicity".

Thanks again people, I now have a clearer picture.

I do not think that the standard of care here is "relatively fool proof once turned." I think that the appropriate standard is "an outside professional could easily fix the system when something goes wrong - a pump fails, a controller burns out, etc." and that "the homeowner can adjust the system to adjust the home temperatures to something more to his or her liking."

Jeff

Have struggled with the same question. Low tech solution: Baths and bedrooms are on north side on a separate heat zone. South side thermal mass floor is only heated by boiler on very cold, non sunny times. Other than that we will live with the temperature swings in the south great room. we will have some fans to move warm air from hot south room to north bedrooms, but will not try to move slab heat with water.

If the solar gain area's were on a separate loop, with separate sensor then couldn't you control that area's heat that way