Solar system components
When you start to think about a solar system, you have to remember that the industry is relatively new in Canada. It has been used in Europe for decades, but its penetration on this side of the Atlantic has been marginal until recently. That means that you have to be conscious that some of the product on the market may not have been certified for use in Canada. The components that were installed in our house and that I will be speaking about below were all CSA approved and the “non-packaged” installation proposal that prepared was certified as compliant with the Ontario Building Code by a professional engineer.
The solar collectors we use in our house are the CAREarth Vacuum Tube Solar Collector SJ Series Heat Pipe Technology. This technology has been optimized for colder northern climates where solar radiation levels are lower. A brochure for the SJ Series in .PDF format can be found here. We installed 2×20 tube collectors and 1×10 tube collector (50 tubes) in series on our house which amounts to roughly 5 square metres of absorbing area. This should be plenty for the hot water needs of a family of 5 people (including teenagers), but when you divert heat to a swimming pool in the summer months, you will find that you still need to augment your hot water heating with gas or electric.
The controller that we use to decide when the circulation pump should be activated is the Resol DeltaSol (TM) BS. It is the brains of the system and it decides when enough heat exists in the collectors to add to the heat in the water tank. It also monitors the temperature in the tank to make sure that it does not overheat and when it gets too hot it can divert the heat to another unit (like a pool, an ambient heater or a solar cooling unit).
Our unit has 43 programmable parameters and can deal with just about any situation. One example would be that if the temperature approaches the freezing temperature of the glycol in the system, the unit will turn on the pump for a few seconds to effectively steal heat from the hot water tank to make sure that the system does not suffer pressure damage due to freezing of the antifreeze. This is a useful feature in a climate like the ones we find ourselves in.
To do its work, the collector uses a variety of heat sensors to control pumps and valves which change the way fluids flow within the system.
When we installed the system, we were as concerned about safety and about wasting water as we were about wasting energy. We were informed by the installer that he had to install components to isolate the house’s water system from the municipal system (more about that later) and to be able to handle high pressure or high heat conditions in the system.
The first decision we had to make was to decide which option to choose for dealing with possible overheating of the system. Overheating of the hot water tank occurs when a household doesn’t use enough hot water during a period of high sun. This might happen when, for example, a family goes on vacation to the cottage for a few weeks in July when the sun is hottest and the days are longest. Available options for dealing with this issue include dumping hot water down the drain when the temperature in the system reached an established threshold or using various heat-sinks to remove excess heat from the system.
Automatic heat diversion
Because we do not want to waste water, dumping hot water down the drain (if the system overheats) is not an attractive option. The components necessary to get rid of heat this way are always installed as a failsafe but we wanted to use rather than lose the excess heat and we definitely did not want to waste the water so we opted to use a multi-heat sink option for dumping excess heat from the system. We installed two separate heat sinks … a standalone room heater in the basement for use during the winter months, and a pool heater for use in the summer months. To operate these two heat-sinks, we installed a Honeywell VC Series 3-way Balanced Hydronic Valve. When the temperature in the tank exceeds a parameterized limit, the controller instructs this valve to automatically divert heat from the tank to either the pool heater (in the summer months) or to the basement heater (in the spring, fall and winter months).
The photo at right is a backflow preventor that isolates the water supply in the house from the municipal water supply. The reason that this is needed is that the solar tank has a “potable / non potable” water interface. What is a potable / non potable interface you ask? Basically, potable just means drinkable. A solar thermal system works by transferring heat between two loops of circulating fluid. The cold loop is the normal water supply to the house which enters the cold intake of the hot water tank, is heated in the tank and then leaves through the hot water connection at the top of the tank. The hot loop is a loop that takes cold fluid (glycol based) from the tank and pumps it up to the collectors on the roof where it is heated and returned to a heat exchange unit installed in the tank. The heated fluid in the second loop transfers its heat to the water in the tank in this heat exchange unit. The heat exchanger in the tank is an interface between potable water (the normal water supply) and non-potable propylene glycol – hence the term potable / non potable interface.
While the heat exchange unit is supposed to keep the two fluids apart, there is always a possibility that the exchanger will leak and some of the glycol may get into the water. While this isn’t really a problem with propylene glycol (which is an “edible” product) it could be a problem if the installer or the home-owner used the poisonous ethylene glycol. In a normal neighbourhood the municipal water supply sloshes into and out of a house based upon the relative pressures of the two systems. This means that if an installer used the wrong glycol and the heat exchange unit leaked, the municipal water supply could be affected. For this reason, the building code insists that the house be isolated from the municipal water supply by using a one-way valve that allows water to slosh into the house, but does not allow it to slosh back out again.
Pressure management tanks
So what to do? Well, the way that this is handled in an isolated home is to install a pressure release tank in the system (see photo at right). These tanks contain a diaphragm or bladder that isolates one end of the tank from the other. One end of the tank is attached to the plumbing system and the other end of the tank has an air valve, similar to the one on a car tire. The air valve is used to pressurize the tank to the normal level for the plumbing (60 psi). This forces the diaphragm to expand toward the plumbing end of the tank forcing any fluid from the tank. When the pressure in the system rises, fluid is forced into the tank, pressing on the diaphragm and compressing the air behind the bladder. This effectively increases the pressure in the tank and reduces the pressure for the remainder of the system. In our home, we have one tank associated with the glycol loop and a second tank on the water loop.
Well that is it for now. I will talk about some of the other components in future blogs. Until then, get going and get green.
- Solar Water Heating in Ireland (allhome-improve.com)