Thursday, July 12, 2012

Solar Water Heater

Building of a Solar Water Heater.

This article is a description of a closed-loop Solar Water Heater (SWH) I have built and installed at my residence. Although today, the prices of SWHs have gone down in price, (also thanks to the government rebate), I must admit and others who bought a ready-made SWH will agree with me, that the quality of some brands has also gone down! Besides cheap workmanship with some Chinese brand SWHs, one thing I cannot stand is that most of the imported brands can't withstand Malta hot Summer or better have to be manually protected during the Summer months to reduce stress on the system. It's understandable that in Summer (or the warm months), the demand for hot water decreases and therefore only a small percentage of the daily heated water is used, thus hot water accumulating daily in the tank with an increasing temperature. This will pose more stress on the SWH storage tank and other components, resulting in a reduced lifetime! To overcome this problem, most of the installed SWH collector plates are covered in Summer to reduce heat absorption, heating less water and therefore reducing stresses. The SWH described here does not need to be covered, and all components are protected from this problem!

A good reference for starting to learn the basics on SWH can be found on the Home Power magazine web site. Please do visit the site since it will give you a good description of all the components I have used in this system.

System Description:
The system I opted for is a closed-loop, meaning that the sun will heat a liquid which in turn will heat the water though a heat exchanger. Although a closed-loop system is not a requirement for the country I live in since we don't have freezing temperatures and there is no need to empty the system at night, I still opted for this slightly more complicated system for the below reasons;
1) I wanted my home-made solar collecting panels and storage tank to last longer. This can be achieved by NOT passing water through the collector/storage tanks circuit but instead passing glycol. Glycol will not rust and prevents limescale from forming which has the side-effect of decreasing the system efficiency.
2) I did not want my SWH storage tank exposed to the elements, simple because I want it also to last longer. Using a closed-loop system, the storage tank can be easily placed away from the solar collectors
3) Decrease heat lose especially in Winter. In fact I placed the storage tank inside.
4) The SWH I've designed will have two three energy sources;
 - The sun, which will heat up the collector and the storage tank.
 - Log fire. I'll be utilising unused/escaping heat from the fireplace to heat up the SWH storage tank.
 - An electrical element which will be used when the above two sources are not enough

The pictures below detail the construction/function of the SWH.

The picture below is displaying one of the solar collectors without the tempered glass. The horizontal top (outlet) and bottom (inlet) pipes are 1/2 inch while there are ten 3/8 inch vertical laid copper pipes fixed to a matt black painted galvanised sheet. The total area of each collector is 2 m3.

The image below is showing the two solar collectors mounted facing South with a total collecting area of 4 m3. (The collectors in this picture are not yet connected). The supporting frame used is 3mm
galvanised steel.

The below image is displaying the underneath of the SWH tank. Connections:
1) Two connections inlet/outlet are used for the closed loop solar collector (heat exchanger circuit 1).
2) Two connections inlet/outlet are used for the closed loop fireplace source (heat exchanger circuit 2).
3) The middle large hole will house the electric 2KW element.
4) The other large hole will house the zinc anode.

The image below is showing the interior of the SWH storage tank. Notice the two circuits (left & right interlaced). The vertical copper pipes are about two-thirds the length of the storage tank.

The image below shows my neighbour Mario doing the copper brazing work on the tank circuits. He's a professional machinist by trade and therefore all this was a  piece if cake for him!

Sketch of all the SWH components connected...

The below image is the 'brain' of the system. Its all controlled by the Steca TR0301 controller. I won't be detailing here all the specifications of this controller however at a glance;
1) Can monitor 3 separate temperatures; Solar collector, SWH tank top and bottom water temperatures.
2) Pre-set with a starting differential temperature of 8°C
3) Cut-off differential temperature of 4°C
4) Cut-off maximum tank temperature of 60°C
5) Holiday function.

The below image is displaying the SWH components.
 - Top left is the 18 litre expansion tank. When the pressure inside the system increases due to high temperatures, the glycol moves temporarily into this tank to relief the pressure.
 - Below the expansion tank is an MCB box. An MCB is used to manually switch the electric heating element while the second MCB is used to power the differential controller.
 - Next to the MCB box is the Differential Controller.
 - Next to the Differential Controller is the internal circulation pump. This pump is switched on/off automatically by the controller and is used to circulate the glycol around the collector panels and heat exchangers inside the storage tank.
 - On top of the circulation pump is a small pressure gauge, measuring the pressure inside the closed-loop circuit.
- Below the pump are three values used to prime the closed loop circuit.

The below image is displaying the SWH storage tank pipe connections.
- The two top connections are the inlet/outlet to/from the solar collectors closed loop circuit.
- The next two connections are the inlet and outlet for the hot water system.
- The bottom connection is the 'hot' feed to the washing machine.

The below image is displaying the SWH storage tank with all the external components (on the left) and the inlet/outlet piping on the right.

The system has been in operation since 2008 without any problems. The sun does provide all of my family hot water requirements for a full eight months, while the remaining four winter months are assisted by the electric heating element.
Hopefully I will get all my hot water without using electricity including the winter months, since I'm currently working on the second circuit / heat exchanger to heat also the water using heat from the log fireplace. I'll be posting an article once this is ready and in operation.