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Space Heating Using Solar Thermal Technology

Space heating can be done passively or using active mechanical systems. Here we are going to talk about solar thermal hot water systems to provide space heat. We also sell and install Solarsheat hot air systems to use for supplemental space heating.

There seems to be an abundance of mis-information, from otherwise reputable sources, regarding the use of solar thermal panels to provide space heat to a home or business located in New England. Our best guess to as why this exists is simple, the technology has changed faster than some entities ability to keep up, and adjust their marketing materials. In addition a reputable solar installer is never going to jump in and promote a product until it has proven its capability and reliability. Since you cannot do space heating here without a high quality evacuated tube, such as Thermomax, some installers just say it cannot be done.  In addition unfortunately the majority of Maine's heating systems are "high temp" meaning the system was designed to work with a incoming temperature of 180 degrees.  Low temps systems require 80-120 degree water and can work with for solar thermal heating.  With a high temp system, in Maine, we just cannot consistently generate 180 degrees during the short winter months.  

solar for warehouse

Warehouse radiant heating with solar is comfortable, cost effective, and produces zero emissions.  Since the floor is warm, so are the employees, without the expense of trying to heat a huge volume of air.

With that said, we can tell you without a doubt that solar thermal space heating does work in New England. In August of 2009 Solaris was extremely excited to announce that we had become the authorized dealer for the Infloor/Thermomax product line for the Southern Maine area. This product has the ability to collect enough solar energy during our short New England winter days to generate enough hot water to provide the majority of heat for your home or business.  Globally, space heating (and cooling) has been done for well over 15 years.

Thermomax is a “true evacuated tube” and provides the ability to collect much more solar energy in the short days of winter when compared to other types of collectors. Three key areas make this tube different:

  1. The tube construction; a vacuum enclosed by a single layer of glass.  The heat pipe resides within the vacuum so it is protected from outside temperature
  2. The selective coating on the collector fin to gather direct and difuse radiation. 
  3. The industry's highest quality glass and vacuum process. 

Given the harsh short days of New England winters, flat plate collectors and even most hybrid evacuated tube systems (the ones with 2 glass walls)  just do not produce enough BTUs to heat your home. Since the weather is unpredictable it is important to take advantage of sunny days to get the storage tank temperature as high as possible. A tank of 180 water generates more space heat than a tank of 140 water.

If you are told by a solar installer that solar thermal cannot be used to provide space heat, to some extent they may be right. If they do not have the right product to install, and cannot properly design the system, it will not generate enough Btu’s in winter. Putting up additional panels can help with low collection during short winter days but it will also raise the system price and create excess summer heat. Many tubes, and all flat plates, do not have the ability to generate the high temperatures that a Thermomax tube can. Solaris has the experience and expertise to design a system for your home and your BTU needs, and we will give you a written guarantee of performance.

So how does it work?

If you are fortunate enough to have radiant floor, low temp baseboards, or radiators for heat in your home now, today is your lucky day. Solar tubes will routinely provide water at 80-120 to pump through your existing radiant system. A very large hot water storage tank will be installed. Your current system, or possibly an on demand water heater, will be put in place as a backup for days when there is not sufficient solar energy. We know that in the short days of December and January, the backup system will be needed at times. 

If you are like the majority and have hot water baseboards (that need water at 180), forced hot air, wood/pellets, space heaters, etc. then the task is bigger. Once again a large storage tank and backup system needs to be in place. We will retro fit your home with radiant floor heating. Installing the radiant track is not hard and can be a DIY project. Most of us would be quite happy to have our half of our heat for free. Solar systems are easily expanded, provided you initially install the correct size tubing and controllers.  If you want to stick with a high temps system then we design the solar thermal heat system as a supplement, or pre-warm, meeting only part of the heating needs.

emission plate

There are many options for retro-fitting depending on the type of construction and access available. Some ideas are outlined below. What makes much of this now possible is the availability of radiant panels that are only 5/8 inch thick. These panels can be installed almost anywhere.

Radiant Floor Heat

  • Install radiant track emission plates on basement ceiling between joists turning your first floor into a radiant floor.
  • Temporarily remove carpets and install 5/8” thick boards, replace flooring.
  • Install boards vertically on any wall in any room.
  • Use low temperature radiators, or baseboard, in the rooms
 

If you have a forced hot air system it is possible to use your solar generated hot water to help heat your building. A/C systems use a coil within your furnace to cool the air. Hot water can be used to warm the air.

In any case you should take steps to insure you have proper insulation, caulked to minimize any leakage, and performed all reasonable weatherization upgrades before investing in any solar energy system. Normally efficiency improvements will have a quicker payback that solar thermal. We highly recommend having an energy audit done. The more efficient the building the smaller the solar system needs to be.

Baseboard Heating with Standard High Temperature Baseboard

It is possible to use solar thermal to supplement your baseboard heating system. When we install a solar thermal system we try to use as much of your existing equipment as possible, giving you the quickest return on the money you spend.

One way to often accomplish this is to enhance your baseboard boiler by using solar hot water. Baseboard usually needs 180° water, unlike radiant that uses 120°-130°. But during the warmer months of spring and fall it is often possible to keep they home warm with only 120° water. This is accomplished with “outdoor reset” equipment. These components are added to the existing system to sense the outdoor air temperature and the temperature of the water returning from the baseboards.  When it is warmer outside, and the return line water is still warm the system will automatically reduce the boiler temperature. For each 3° you lower the water temperature you save 1% on fuel. So, going from 180° to 120° will burn 15% less fuel.  Even better is that at times your solar system can help provide the heat to re-warm you heating loop.  In months such as December, with short days, the solar system will not be able to assist with space heating, it struggles to meet your domestic hot water needs. In the summer the boiler is off since you have plenty of solar hot water for domestic needs, and no need for heat. In the shoulder seasons, solar can help heat your home and provides your domestic hot water.  It is not going to make a huge annual difference but it is a fuel saving combination.

Overall using solar thermal with a high temp system is a good fit if you are seeking an environmentally friendly way to heat.  On a cost per Btu there are other options that provide a better value such as boiler upgrades or an air source heat pump.  In warmer climates there are additional options.  

New Construction

Too often we have seen home builders recommend installing radiant heat on the first floor and baseboards upstairs in the bedroom. The reasoning is that baseboards are less expensive. This is completely true only in terms of installation costs.  But if you are the homeowner paying the monthly fuel bills, this normally is a big mistake.

Standard baseboard heat uses 180 water in the winter. Radiant heat needs 80-120.  Since you have to heat your water to 180 for the baseboards you are burning about 15% more fuel.  Residential solar thermal panels cannot provide 180 water consistently in winter when you need it for space heat. So, the boiler is now required to run at 180, burning up your installation savings in no time.  If the entire home is radiant, then solar thermal can provide much of the heat needed for the radiant floor system. Your boiler/backup system would only come on when necessary to raise the temperature to 80-120.  Your initial costs will be higher, but then the sun can heat your home, for free, forever.  Even if you rely on a boiler, running it at 120 vs 180 is going to save about 15%.

There are federal tax credits to builders who install solar thermal systems. Your builder can take this rebate, or pass the savings on to you in terms of a lower price. Not all builders know about this.  There are also rebates for high efficiency “energy star homes”. Of course the homeowner is eligible for the 30% federal solar tax credit.

Myths, misconceptions, and changing technology

Myth: "Solar Radiant Heating is too expensive "

Truth: Radiant is the most cost effective heating choice for homes with higher heat loads, solar makes it even better.

Myth: "Solar Radiant Heating limits floor coverings because of concerns over possible nail holes into the PEX."

Truth: R-values of many floor coverings are compatible, installers are now trained and experienced with radiant, so accidents seldom happen.

Myth: "Solar Radiant Heating will overheat my house because it has poor temperature control."

Truth: Improved slab sensors are more accurate than past incarnations, Warmboard is very responsive.  We highly suggest you build a tight well insulated home.  This will mean your heat load is very small and it is quite likely you do not need a boiler with radiant and that it will over heat.  In these cases we highly recommend an air source heat pump. 

Myth: "Radiant Heating will make the air in my house too dry."

Truth: Overly dry air results from building shell air leakage/insulation problems, not radiant or any other form of heating

Myth: "Solar Radiant Heating cannot be installed in existing homes.

Truth: Warmboard and radiant track allow easy retro-fits.

In new construction radiant floor heat has become extremely popular.  It is cost effective, works great, is “out of sight”, and makes the living space more comfortable since it warms any object in the room not just the air. Traditionally PEX was run through a concrete like slab. Certainly you would not want to have your house torn apart to pour concrete.

Now we also have products such as Warmboard and radiant track. With these outstanding products most homes can be retro-fitted in a cost effective manor, with little disruption to your home. Radiant boards can be installed under existing carpet, we can go to the basement and put radiant track in the joists below the first floor, they can be installed vertically in/on walls, or even in the ceiling. Slab based systems are still a popular method in new homes, especially in areas where you want to maintain a constant temperature all day long. Improvements in the slab temperature sensors help with overheating.

Just imagine, no more dusty, rusty baseboard to worry about, and a warm floor for the kids to play on. Best of all, your heating bills can be slashed by up to 70%.

In new construction products such as Warmboard are very popular. Warmboard is both the sub floor and the bed for the radiant track. It looks like a sheet of plywood, routed for radiant tube, and coated with aluminum that does an excellent job of dissipating heat.  It is not cheap, but saves on the cost of a sub floor, and cuts labor costs dramatically.  These products make radiant much more “responsive” than imbedding PEX in slabs.  This is nice in a bedroom where you might want to lower the heat for just the night.  With Warmboard there is no more waiting for the concrete mass to heat, nor is over heating a problem.  

Warmboard has a great ad that makes their point very clear. It says “your pots and pans are not made of concrete for a reason”.

In slab systems provide the most even heat.  In addition they can run with water temps as low as 80 degrees vs 120 with Warmboard or track systems.  This save about 12% on fuel.  They also retain heat well if there is a power outage.  With a tight energy efficient home you have a very low daily heat loss.  It is quite possible to be comfortable for a couple of days with no power.

Low Temperature Baseboards and Radiators

low temp radiator

Standard baseboard needs water temperatures of about 180. They heat the room through a convection process. The fins inside are designed to flow air and move heat. There are also low temperature baseboard systems with more tubes and fins. They are more expensive per foot but since they can use lower temperature water, you can cut your fuel usage. Low temperature panel radiators are also available and are inexpensive. They are the perfect choice for single rooms, basements, or garage heating.  The home on the right uses a low wall mount panel radiator system. 

Summary

The truth is that a Btu is a Btu. It does not matter if it is generated by a boiler or by a solar thermal system, it can still heat your home. A solar thermal system in Maine is not going to meet all your needs during the short days of December and January and you will need a backup system. Sizing a hot water or a space heating system requires matching the collector output (see Thermomax output chart) to your Btu requirements. When looking at solar output numbers make sure you have data for Maine and carefully compare winter output.

Changing technology and cold weather air source heat pumps

We are big fans of radiant heat but the boiler and the radiant system are expensive.  These days we are finding that adding a supplemental air source heat pump can provide the comfort and money savings most families are seeking at a much lower cost. 

If you are building new we cannot stress loud enough that you need a good builder than truly knows how to build an energy efficient home.  If you spend an extra $10,000 on the shell then you will not need an expensive radiant system  An air source heat pump can provided the space heating at a very low annual fuel cost.  We are happy to provide referral for some really great builders.

 

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Solaris

600 Riverside St.

Portland ME 04103

(207) 797-0979

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