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Outdoor weather/solar compensation

Simply Rad
Simply Rad Member Posts: 190
I have been thinking about how efficient new homes are getting build. Here in Steamboat Springs, Co we have a new building code requiring the use of continuous insulation on the outside of the building along with insulation inside between the studs. Some of my project end up being R20 below the slab, R40 in the walls and R-60 in the lid. But still LOTS of glass, and glass that emphasizes the view, whether its a wall of glass north or south. Here in Colorado we have a lot of high altitude sun. Not only do we have a lot of sun, but have have very large temperature swings. Last week it was -15F in the morning and 30F in the afternoon. I find that very few architects ever consider passive solar design, because the clients wants all the views. Therefore, even with low mass radiant floor systems over heating is a big challenge. I have so many 2nd homes with really expensive blinds to slow the solar gain.
I have been thinking about how powerful the OTS (outdoor temp sensor) for a radiant floor system. It provides the ultimate in comfort and efficiency. But what if I install it on the south side of the house. In the day time here it can be 0F and feel warm because the the high solar radiation at 7000' + altitude. So what is the real feel for that? Well I think with the homes being so well insulated, that the north rooms would stay warm. They would also stay warm because nature want to balance and heat in the house would travel from warm sunny great rooms to cooler areas of the house. I am thinking about installing a second OTS wire on the south side of the house along with wire on the north side. Then trying an experiment with the 2 options.
I have always done what I have been told and install it on the north side of the house but knwo I am questioning this

In my mind this is simple way to provide weather/solar compensation without getting to many electronic involved. What do you think? Jeffrey
Jeffrey Campbell


  • Jamie Hall
    Jamie Hall Member Posts: 23,668
    Dealing with excess solar gain can be a real problem -- or an opportunity for a solution. The trick is to handle as much of it as possible so that the excess -- during those bright sunny days you folk get -- is stored somewhere, and a high mass radiant slab is pretty close to ideal for that.

    One of the things I would do if faced with the problem would be to zone the slab so that spaces which get excess gain were separate from those which get little or no gain, and use a slab sensor or sensors to circulate warmed water from the gaining areas to the cool areas -- whether there was a boiler operating or not. This wouldn't cure the problem -- but it would reduce it, and enable you to store a good deal more heat in the slab than your otherwise might be able to.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,498
    What about a radiation sensor. The Resol solar controls accept a "sun" sensor option. They are generally used to turn on solar systems where wiring to the collectors is unavailable or defective. No reason it couldn't turn something off.

    I think Dale up in Bozeman played around with radiation sensors as drainback triggers instead of thermal, pipe sensor, since the pipe is empty after drain back :).

    Maybe even a simple light photocell with override if temperature falls?

    We had a few up at Caleffi, if you are interested in playing with one.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,546
    It’s funny how the sun is so much more intense at the higher elevations. I remembered out in aspen skiing how intense that was. Cold, but you could go with out a jacket, and the snow wasn’t melting. Strange effect.

    I think the key controlling the gain, and loss with good quality insulating window treatments. Controlled by some radiation, and temp sensors to automatically open, and close. With an override for enjoying the views.

    I know the new mercy hospital I worked on had solar tracking shades on all the south glazing of the first, and second floor atrium. About 60k not including installation.

    Mostly used to control gain in summer. I’ll try to find out how, and what controller is used. What it tracks, indoor temp, solar gain, or a combination.
  • Simply Rad
    Simply Rad Member Posts: 190
    Thanks for the input. One thing to realize is that I care more than the customer about saving energy and comfort. I have some of the 1/4 percent wealthiest clients who don't care other than it works and they have great views. All of the home have window treatments for the sun, but still when you have too much glass and not enough mass to absorb the heat you over heat. Even with $250,000 window solar shades the homes heat up. You have to understand I call some of these homes fish bowls because of the amount of glass. I am thinking about maybe not turning off the system with the solar radiation sensor but using the OTS to lower the SWT. This way even if a north facing back room needs heat it still can get alittle.
    The hard part is figuring which South aspect to install the OTS. The SE aspect will turn it down quickest....S will turn it down most of the day and SW will turn in down in afternoon which is when we over heat the most.

    HR I would like to have a solar radiation sensor if you have a few.
    Simply Radiant Heating
    Box 775733
    255 River Rd
    Steamboat Springs, CO 80477

    Thanks Jeffrey
    Jeffrey Campbell
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    I think combining a low volume hydronic air handler (which also brings in fresh air and can economize on mild days) with a slab operated at a lower water temp, would work well. The hydronic air handler could be zoned. OR install smaller loop, only in the middle of the room, less on perimeter.

    Other option could be fin tube zoned room by room pipe in a series.parellel arrangement to the radiant floor heat so boiler efficiency is maintained. Delta T could be increased to 35-40F at design.

    Or a combination of all 3.

    In floor recessed fin tube in front of windows directly with a sensor that detects solar gain to enable it.

    But it needs to be relatively simple and mostly passive if possible.