Solar water heater systems combine several innovations to transform cold water into hot water. Solar water heaters can deliver hot water for almost no cost for most of the year. However they are usually coupled with one other water heater type in order to provide a steady supply of hot water even in cloudy winter days.
What are the general system design requirements
There are several factors that influence the type and complexity of a solar water heater. The desired temperature and amount of water that you want the system to produce is an obvious factor. The minimum requirement is typically determined by combining the temperature and amount of hot water requested in the winter.
Since in the winter the system is at it’s lowest output level it makes sense to start from there. Another important factor is the change in ambient temperature between seasons. The bigger the change the more difficult it is to find an appropriate solar water heater system. Also, changes in temperature in between the day and night cycle is another factor.
What about freezing and overheat protection
The last important aspect involves potential water heater problems concerning the solar heater system. The collector fluid or the potable water can either freeze or overheat. Freeze protection is generally ensured by use of antifreeze in the heat transfer fluid. Overheat protection occurs when there has been no usage of hot water for a few days, since the fluid in the collectors keeps heating.
What are the differences between types of solar water heater systems
There are two main ways to characterize solar water heaters. The first classification is active or passive. This refers to how the solar water heater circulates the heat-transfer fluid. An active solar water heater system uses an electric pump to circulate fluid, a passive system doesn’t.
The other way to classify them is as direct or indirect. This refers to an open-loop system or closed loop system. Open-loop systems circulate water through the collector. Closed-loop systems use some form of heat-transfer fluid to collect heat and then transfer the heat into the water using a heat exchanger.
What is the difference between passive and active systems
Passive solar systems rely on heat pipes to circulate water in the system. They have a relatively low cost and require very low maintenance, however the efficiency is also much lower than their active counterparts, and overheating and freezing can become big problems.
Active solar heater systems use several pumps to circulate water or some type of heating fluid. While the cost is only slightly bigger the advantages are significantly higher. The storage tank can be situated above or below the collectors, allowing much needed system design freedom as well as the possibility to use existing storage tanks.
The storage tank can be hidden from view and can be kept in conditioned space, thus reducing heat loss. They also have the possibility to add drainback tanks. Overall superior efficiency and control through a display panel make them much more reliable choices.
What is the difference between direct and indirect systems
Direct systems are cheaper than their counterparts and have superior heat transfer. However they have many drawbacks. There is almost no protection against overheat and freezing. This makes them unsuitable for cold climates. There’s also a fair chance that the collectors will accumulate scale.
Indirect solar water heater systems have one of the two most common heat-transfer fluids – Antifreeze and water – and use this fluid to transfer heat from the heat exchanger into the water. They are slightly more expensive than direct systems but they come equipped with overheat and freeze protection.
Existing solar water heater systems include many combinations of these characteristics. The perfect solar water heater is dependent on your location, exposure to sunlight, overall climate and many other factors yet, if taken the time to find it, can bring a big dent in your energy bills.