The Ecobob member's forum: where members discuss, discover and network all things green and eco.

Keyword Search

future proofing for solar hot water heating?

Home > Chat Forum > Building design, construction and renovations > future proofing for solar hot water heating?

future proofing for solar hot water heating?

Posted 11 Mar '12 06:21 PM

I would like to add the ability to be able to retrofit my new build with solar hwh at a later date. For now, we will most likely use a standard electric cylinder. The cylinder would be situated roughly in the middle of the house, on the lower level of a two story build.

would it be possible to do this? what type of cylinder to I need? any recommendations to makes/models what size conduit to send to the roof? are there any other requirements?

Re: future proofing for solar hot water heating?

Posted 11 Mar '12 08:13 PM

To gain max benefit from a solar heated system the cylinder should be sized to allow 2 full days use without running out of hot water, thus for a 2 person house you require approx 300 liters. A big cylinder full of water is heavy make sure it is well supported. If using the electric element as backup then get one with the element fitted in the top 1/3rd of the cylinder, this allows a good proportion to be heated by the sun, when you fit your panels, there is little point in attempting to solar heat water already warmed by the element. Whomever is supplying your system should be able to supply you with other required details. From experience, place the cylinder closest to the point of most usage, this will be the kitchen or a bathroom. In our house I used 2 cylinders, one directly under the kitchen sink floor and the other in the center of the house supplying the on-suits and main bathroom, laundry.

cheers Mike

Re: future proofing for solar hot water heating?

Posted 11 Mar '12 08:20 PM

The shorter the distance between the roof and the cylinder the better: otherwise you lose a lot of heat (even if the pipes are lagged) between the cylinder and the solar collectors when the system is heating, and the pump is circulating the water between the cylinder and the collectors - so the cylinder shouldn't be on the bottom storey.

But the cylinder needs to be near the point of the most often use of hot water (otherwise you spend a lot of energy heating pipe runs every time that particular tap is turned on). So would you be able to put the cylinder close to the most often used hot tap if it was on the tap, while meeting the requirement above as well? (If you need hot water for the kitchen sink or something, put in an electric under-sink cylinder - so your hot water losses are almost eliminated.)

Pre-piping of solar hot water pipes does save money - ask a few suppliers what size to pre-plumb to (ring them up and they might raise some other issues for you to think about).

The size of the system depends on how many people live at the house - a rule of thumb is 50 litres per person per day plus 20 litres for the house. So if it's a big house with 4 bedrooms, then 220 litres is the minimum system size. The more storage you have, the more solar energy you are able to capture - BUT the higher the cost (and you have to build a larger hot water cupboard: changing the hot water cupboard later may mean the system costs are way beyond what savings you will ever recover.)

The installation cost of swapping a cylinder later, even if it fits the cupboard, is probably more than the difference between buying a standard electric cylinder today and buying a solar cylinder today (the solar cylinder will have additional features such as a higher temperature rating, a second set of connection ports for the solar connections, perhaps a coil, and more likely to be stainless or copper and not glass lined like you would have for standard electric cylinders that operate at lower temperatures).

These are just come of the considerations - suggest you ring up suppliers and have a chat with them - some of them actually answer their phones!

Re: future proofing for solar hot water heating?

Posted 11 Mar '12 08:40 PM

Yes definitly a cylinder designed for solar WITH a heat exchanger coil. Pumping your hot tap water directly through the panels is a no no and not allowed in many countries for good reasons

Re: future proofing for solar hot water heating?

Posted 12 Mar '12 12:43 AM

A heat exchange coil is an expensive item, and significantly reduces the efficiency of a solar system.

There is nothing wrong with tap water going through a solar system, apart from the risk of freezing.

A solar ready cylinder normally has a couple of extra ports for solar connections - plus an element hole near the top. It must be made out of stainless steel (mains pressure) or copper (low and medium).


Re: future proofing for solar hot water heating?

Posted 12 Mar '12 10:22 AM

Thanks for the feedback - I had never thought about locating the water cylinder upstairs and as it turns out, there is a pefect cupboard for it which is also handy to the kitchen and bathrooms.

I think i can now speak to some vendors and get some specifics.


Post Your Own Comment