Hi Shane,
I was very interested to read your comments. I am putting in system similiar to that which you describe (solar and UFH). My house is 2900 sq ft.
Based on this size what volume of a buffer tank and how many tubes would I need.
What would the approx cost of the tubes be?
Many factors will have to be considered before designing this system and whether or not it will be worth installing in the first instance. Great care must be taken in order for it to be fit for purpose and I would only recommend going down this route if many considerations are catered for. It is not just a matter of sticking a buffer tank in with 60 tubes and off you go. Many other parameters must be installed, otherwise the gain will be quickly outwayed by the losses:
1. Are you installing UFH both downstairs and upstairs? If you are combining UFH with radiators, I would not have the radiator circuit drawing its heat from the buffer tank as this will cool the buffer too quickly.
2. You will need a cylinder for DHW and that can bypass the buffer tank in winter months, taking its heat directly from the boiler. In summer, it should take its heat from the buffer. This will take a good design and control system. It will be complex, in that all certain situations must be catered for, for example:
Buffer tank is cold, UFH heating requests heat, buffer stat will not allow circulating pump to function to stop cold water pumped through UFH circuits, it calls in back-up heat source and switches on pump when temperature of buffer reaches pre-determined minimum temperature.
3. What is your back-up heat source, i.e. oil boiler, gas boiler, ground source heat pump, air to water heat pump, etc.?
4. The size of the buffer tank will depend on how much of an energy store you will require. The larger the energy store, the larger the input of energy you will require. Larger is not generally better as this will have an extremely poor efficiency during summer months as the buffer will only be used for DHW. I find that 500L is an accpetable, viable and economical option. A 500L buffer tank with a
∆T of 30°C will have a thermal store of approx 18kW.
5. What is the overall heat loss of the property in watts/m²? The lower this value the longer the buffer tank energy will last.
6. The amount of tubes you will require to heat a 500L buffer tank will depend on the specification of that tube, the azimuth in relation to south and the pitch of the roof that they are to be installed upon. Do not use flat tube for winter solar gain. Flat plate absorbers are not in a vacuum therefore surrounding ambient temperatures will kill the solar gain. Only select tubes for winter gain.
7. The cost of tubes and installation, etc. will very much depend on the quality of the materials used and of course on the competence of the installer. Other factors will be type of materials used, such as copper pipework versus stainless steel, glass lined stratified buffer tank versus standard, basic control system versus high end, etc. etc.
8. Is your UFH system installed already or in the design process? Some of the controls I speak of can be encorporated into some UFH systems, such as Heatmiser. A secondary control system will of course have to be installed at the buffer tank side, encorporating three port diverter valves, a number of monitoring temperature probes at different levels of the buffer and four circulating pumps, some of which will be standard and others being self modulating.
9. Where will the buffer tank be located and how far will this be from the UFH manifolds?
Apologies if I cannot be too specific, but the design of this system is complex and really cannot be done over a forum.
Finally, if you PM me, I can email you a layout of what I am talking about. Hope this helps.