Solar radiant heat project begins

[cartod]

Radiant heating is great, I've had it for 23 yrs. Don't have the solar part just a boiler with a 120 gal storage tank and heat exchanger in it for domestic H/W. You don't need your floors very hot to be warm, when your floor gets too warm, the whole house is HOT! Your feet are warm and then you look at the thermostat on the wall and think it should be hotter than it reads. Make sure you have back up power/genset to run your circulating system because after a couple of days with no power you start getting cold, so for short power outages you can get by OK. It's a totally different feeling when you walk in from the cold and you get that radiant warmth that just settles in and isn't stifling like a hot dry furnace system can be.

Some good info, thanks. We cant wait until next year to put our system into operation. A few questions about radiant heat. Does the heat rise like hot air and make it warmer on the ceiling than the floor? Do you need to use a humidifier to keep the air from getting to dry? Do you still use some type of air circulation to clean/filter the home air?

 

[beeforty]

Heat rises but not like when a blower is running. Plus with air moving there is a cooling effect you don't have with radiant heating. The air doesn't get as dry as with a furnace at least not in Santa Cruz. We don't have any allergies so aren't bothered by dust etc.

 

[Raspy]

My system has now been running for about two months. I want to stress that there are a lot of ways to do radiant and keeping it simple, with good efficient collectors, is a very good idea. Here are a few of my specs:

Our altitude is 5,000', the house and garage combo is about 2,800 Sq ft, I have (6) 4X10 collectors. The temp at night is averaging about 20-25 degrees, but has been colder and a few nights warmer. We have a few cloudy days, but mostly very sunny. My floor circulator runs all the time now as the system is still temporarily hooked up with no thermostat. The collectors use pure water and drain back to a holding tank whenever the system is not collecting. The floor water loop and the collector loop are separate, so the collectors can run and add heat to the floor loop with a heat exchanger, but can also shut off and drain down while the floor continues to circulate. I can also start the boiler and add heat to the floor if I want to during very cold periods or if I want to work in a very warm house. My slab is 8 inches thick.

My system is keeping about 60 cubic yards of concrete, sitting on uninsulated ground, at about 55 degrees average. Not having insulation under the slab means more mass to warm up. My house was not insulated until last week so there was a lot of loss. I did run the oil some, but only during bad weather.

With no boiler running the floor has settled in at 55 degrees average. Perfect for working on the house in a tee shirt.

Last year with no solar the floor was about 25 degrees. Everything froze in my refrigerator and my feet would actually stick to the floor if I came in with wet shoes.

I'm expecting in a month or so that the floor temp will get up to about 65 degrees and this is an average thermostat setting for radiant heating in most homes.

I have no additional storage at this point, but will have at least 400 gallons and maybe 500 gallons when I'm done. Summertime will have an excess amount of energy and I can envision endless showers for free.

I know there is a lot of hype and a lot of opinions on solar. Many want to make it complicated. It is really quite simple if you can get the straight scoop and follow a few rules. It's simple heat transfer, heat preservation and freeze protection. I have 35 years experience designing and installing the simplest and most efficient designs I could come up with and am now just having fun with it. I'm a big solar advocate and love seeing individuals make their own systems, but a few basics must be followed for good performance. In slab radiant is the best possible way to deliver solar heat because it runs at the lowest temperature.

Here are a few guidelines:

1 Decide on the freeze protection system first. Drainback is very efficient, low cost and the most reliable.
2 Design the system to cool the collectors, not heat the water. Remember that the lower the temp, the higher the efficiency. If you cool the collectors effectively, you will remove the greatest amount of energy from them. A larger amount of storage will be more affective at cooling, and therefore more efficient overall. It will gather more energy from collectors that are running at a cooler temp. Don't try to store a little bit of hot water, try to store a lot of warm water.
3 Spend your money on more surface area of high quality flat plate collectors instead of tracking or concentrating systems. (refer to number 2)
4 Keep your delivery temperature as low as possible. In slab radiant is way better than baseboard, for instance.
5 The mass of the slab is very helpful in storing energy, reducing the load on the storage tanks and reducing the use of backup fuels. Proper programming of your thermostats will really increase comfort while reducing backup energy use.
6 Don't use a Nest thermostat, but use a standard programmable model with four settings per day.
7 Always use a differential controller to run the solar instead of a timer, heat sensor or other method.
8 Keep it simple! Spending huge amounts of money on complicated control systems or expensive and unnecessary equipment is a waste. Spend your money on good collectors and lots of storage. Those are the things that make the system really work. The rest is fluff.

 

[Raspy]

Some good info, thanks. We cant wait until next year to put our system into operation. A few questions about radiant heat. Does the heat rise like hot air and make it warmer on the ceiling than the floor? Do you need to use a humidifier to keep the air from getting to dry? Do you still use some type of air circulation to clean/filter the home air?

Radiant heat doesn't rise, exactly. It first warms the floor and feels nice to the touch. You feel warm because you are walking on a warm floor in a cool room. Then, gradually, the walls and ceiling and furniture warm up too, from the radiant energy. Then convection currents set in and the warm air rises. If there is a second floor, it will be warmer than the lower floor if there is no door on the stairs. By then it has probably run too much or at too high a setting.

Humidity can be higher in radiant houses because there is no air circulation and no escape for the humidity to the outside. It's best to have a bath fan to remove some excess humidity or even an open window sometimes.

Radiant does not stir the air so kitchen and bath smells do not go to the bedrooms or other rooms. Dust does not get stirred through the house so people with allergies love it.

It's easy to have separate thermostat zones in different rooms and often houses have 6 or maybe 14 thermostats. Since the air is not pumped around the house they can all be different temps.

Radiant is silent since there is no wind blowing out of registers. This also means the temp in rooms is even. No cold drafts from blowing air. Remember, blowing air on a body causes evaporation. Evaporation causes cooling (evaporative cooling). It's hard to warm a person comfortably while evaporating moisture at the same time. Radiant does not do this and is inherently more comfortable. Plus you get direct conduction into your feet from a warm floor. Warm floors are much more comfortable than cold floors. Forced air does not warm the floor.

Radiant has been around for a very long time, but not many people are familiar with it and it seems odd at first glance. It has been continuously installed since the early '50s in many thousands of homes and is constantly gaining in popularity.

Forced air might be cheaper to install than radiant, and it's better than a floor furnace, but it is a very poor way to heat a house. People consistently tell me their favorite thing about their new home is the radiant heat. No one has ever said that to me about forced air.

 

[1bush2hog]

Thank You Raspy for the info! Sounds like you have a great system.

 

[cartod]

Indeed. Thanks Raspy. But, I do have another question. Actually a scenario. So, you are in the middle of winter, floors are heated up and doing there job, and you have a winter warm up. Now you have 60 yards of hot rock underneath you and its 65 degrees outside. How do you cool the house off? Air Conditioner?

 

[deezler]

^ it's not like the slab is 100 degrees or something. It only needs to be just above ambient to provide heat into the house.

 

[Raspy]

Indeed. Thanks Raspy. But, I do have another question. Actually a scenario. So, you are in the middle of winter, floors are heated up and doing there job, and you have a winter warm up. Now you have 60 yards of hot rock underneath you and its 65 degrees outside. How do you cool the house off? Air Conditioner?

The better the insulation the less the interior is affected by exterior heat or cold. One of the problems with older non insulated homes and radiant is that they overheat during the day because of the Sun's warmth. This also happens to forced air homes. Not so much in my case. I have R42 in the ceiling and R23 in the walls.

In my case I am going for stability. I can set the Master bedroom a bit lower for comfortable sleeping, the garage/shop (1,100 sq ft) at a temp for working on projects, the second bedroom off or very low, and the living/kitchen warmer for sitting around in the evening. If it's a bit cool in the AM and I don't want to run the oil, I start the wood stove. Programming allows a shot of heat to the Master Bath and Kitchen floor for morning bare feet, if needed. But overall, the temp changes slowly and not very many degrees. You need to find a threshold temp that works for you. Say 60 degrees. Then just add a little each morning and little each evening. The usual thermostat setting with radiant is about 10 degrees lower than with forced air.


I don't have this working yet, but each thermostat zone has two thermostats. One only for solar and one for solar and gas backup. The solar only stat heats the house during the day to a predetermined threshold. It cannot start the oil and maximizes the slab storage to reduce the oil heat during the night or early in the morning. The other stat will mainly use the backup stored solar energy at programmed times and start the oil if needed or if I allow it. The solar storage always has priority over oil and, at some preset lower limit, will switch to oil if needed. But, if the solar is collecting it locks out the oil.

See where I'm going with this? Solar first and correctly managed will significantly reduce the backup system. Use temps just high enough for good comfort and set to be right when needed, but not warm at times we don't need it to be. Thermostats used for different functions and used as timers. Simple priority management. A wood stove to add heat and fun as needed.

No solar system, no matter how large, will always be enough to heat in the cold overcast times. Some backup is needed. But, even a modestly sized system is too large in the summer. This is the dilemma. Sizing is always a compromise. A good management scheme is required in the winter, when the system is reaching it's limits. This is not complicated, but requires some thought and design considerations

 

[Beltman60]

John

I really am liking this thread
thanks for all the input
always like to try to learn something everyday at my age

 

[MacLawn]

Looks good, but, I'm as confused as ever about in slab solar heat! Reckon I need to find a video describing how it flows, etc. I'm wanting to install some pipes through floor joists in my crawl space built house. I read something about that. More research...