How to Use Solar Water Heating

Beginner
Batch Water Heater
Batch Water Heater
Thermosyphon System
Thermosyphon System
Direct Forced-Circulation System
Direct Forced-Circulation System
Drainback System
Drainback System
Antifreeze System
Antifreeze System
Pool Heating System
Pool Heating System
Batch Water Heater
Thermosyphon System
Direct Forced-Circulation System
Drainback System
Antifreeze System
Pool Heating System

How to Use Solar Water Heating

Using solar hot water is easily integrated into most people’s lifestyles. Once a system is installed and commissioned, it rarely takes any maintenance at all. The three main uses for SHW are:

Domestic hot water is perhaps the best known of solar water heating applications. Nearly every home uses hot water every day, with the typical U.S. household being around 30 gallons per person per day. This covers showers, dish washing, and clothes washing. Hot water is stored in a tank for when it is needed. An energy efficient household might use less than half of that amount.

Space heating is a lesser-used application for solar hot water. Similar to domestic solar hot water heating, except that non-potable hot water is pumped into either in-floor hydronic tubing, to heat registers or radiators on the walls or baseboards, or to a heat exchanger inside a forced-air heater.

Pool heating is a very easy use of solar water heating technology, and because its equipment is minimal and less expensive, is practically a no-brainer—if you have a heated pool.

Systems

There are several system types for turning solar energy into hot water, and each has its purpose or advantages and disadvantages:

Batch heaters are the most basic—a tank in the sun, though usually in an insulated box with a glass or plastic cover. These are plumbed inline with the domestic water system they serve, no pumps or controls are needed. They make great DIY projects that can be made from any old conventional hot water heater tank. But they do not do well in freezing temperatures—most people will route the water supply around them, and empty them in the winter.

Thermosyphon is the next simplest system. These entirely passive (meaning no pumps) systems rely on the collector being below the tank, so that natural convection moves the hot water out of the collector and to the tank for household use. These systems are also inappropriate for freezing climes.

Direct forced-circulation is similar to the thermosyphon system, but adds a pump and controller. The pump makes it possible to pick up more heat out of the collector. The controller measures when the collector is hotter than the tank and turns the pump on or off as appropriate. These systems also have no freeze protection.

Drainback systems add a tank and a heat exchanger. The drainback tank is sized so that all the water in the collector and lines can drain down into it, when the pump turns off. That way there is no water left in the collector at times when it could otherwise freeze. The water in the system is separate from the household water, so it needs a heat exchanger to transfer the heat from the collector water to the domestic water.

Antifreeze systems are the most common type in climates that regularly freeze. It is has no drainback tank, so the fluid in the collector cannot drain out of the outdoor plumbing. The freeze protection comes from polypropylene glycol antifreeze, so it can stay in the collector after the controller shuts the pump off.

Pool heaters are the final system, and are not used for heating domestic water. Pool collectors are usually made up of many parallel poly pipes sitting on a roof near the pool. The pool water is circulated through the pipes using the pool’s circulation pump, which would be running anyway. The controller operates a valve to divert some of the pool pump’s water through the collector. When not operating, the collector water drains back into the pool.

Comments (3)

Wayne Gale's picture

Anything new on the solar hot water being used in conjunction with refrigerant gases to use for cooling? There used ot be an article about a Japanese fellow who would use the hot water to expand a new found gas that would act as a coolant. I would like to add the fan unit from a split aircon unit and pump cooler water to each room instead of adding the complete split aircon unit. Could probably do something like a chiller unit to produce chilled water but this other methods seems like a better route keeping it closed loop. We generate so much heat from traditional cooling methods, it would be nice to keep that heat contained in a closed loop. I'll keep searching but I think someone paid people off so they wouldn't develop the system. It was there for awhile and now it's gone. If you find an article like this please post it up. All I'm seeing is individual ac units that use the sun and a compressor to heat the water. I want to do all of my heating of water in one location and then pump chilled water through insulated pex to the fan and radiator unit.

mtmtntop's picture

i can offer a little information but need some more from you. i have an endless pool inside my house in montana. i have a 75 evacuated tube array heating the pool and a hydronic floor in the same room. the pool has 2500 gallons. the array can supply 3 degrees F on a sunny day. this array can heat both the pool and the room, although i have a backup boiler in the loop in case the array falls behind. i use 100 below glycol in my array. the array is about 6" tall and 24 feet long and i have it standing at a 70 degree angle to maximize the low winter sun. the array is on a rack that i can adjust the angle, though I don't do that very often. heating that pool with electricity will be very expensive, as in cheaper to go to a health club. plus, any type of electric heater requires alot of power, and usually not generated with pv panels. if this helps you, feel free to ask me questions. i can share some of my experiences. my array has been up and running for 8 years.

bdoyle733's picture

I've moved into a new (built in the early '60's) house that has oil\radiator heat with what I'm told is a very new and efficient oil heater. 6 rooms downstairs and 2 upstairs. There is also an unheated "3 season room" downstairs that I would like to convert into an office for my physician wife. And there is a swimming pool with no heater. The house is in northwest NJ. We use well water, and it's on 5 acres of land (2 acres wooded and not really buildable) with clear southern exposure.
I understand I can't replace the oil heat with solar entirely. So I'm wondering where the biggest bang for the buck is?
- Can\should I supplement the hot water heat with solar so I use less oil?
- Should I just set up the PV radiant heating system for the "3 season room?"
- Should I just heat the pool which seems the most efficient use of solar from what I read here?
- Or should I forget heating and use solar to reduce my electricity dependence on the local utility? (Note there is also a propane fired whole house generator in place in case there's something I can do with that?)
- Or should I forget solar and invest in geothermal (remember the well) or wind?
Finally note that I'm a very healthy 62 years old (feel like 40 :) ) but have no illusions that I have more that 10 - 20 years left, so payback time is a consideration.
I will obviously consult a professional but I've found that people recommend what they know and can sell. I'd like some unbiased opinions from here on what would be optimal to reduce energy payments into the future.

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