Post by cye on Dec 8, 2011 15:32:37 GMT -5
Here's a simple guide to working out how much solar fluid your expansion vessel (EV) will hold when considering the EV pressure settings for a new system (or indeed when servicing an existing system). This volume is useful to know before you start filling your system, mixing up antifreeze etc..
first of all note that the 'EV precharge', i.e., the air pressure in the EV, which is set before the solar loop (system) is filled with fluid, should typically be set at 0.2 bar less than the system pressure you are planning (system pressure=pressure of fluid in your solar loop).
Let's say we choose a target system pressure of 1.4bar, then we should aim for an air pressure (before fluid is added) in the EV of 1.2bar. In this example we'll assume we're using an 18L EV (an EV used in a typical solar thermal installation for a normal household will generally be 12L or 18L capacity)
[1] The pre-charge air pressure is 1.2 bar+1bar = 2.2 Bar absolute
[2] The system (liquid) pressure is then raised, by filling fluid into the solar loop to 1.4bar. system pressure in absolute terms is 1.4bar +1 bar= 2.4 Bar absolute.
So the volume of gas in the EV is now (2.2/2.4) x 18 = 16.5litres
So 1.5 litres of fluid can be expected to enter the EV when filling the system, assuming the above EV precharge and system pressure settings.
when mixing up antifreeze this is a handy number to know. the total voulme of solar fluid you need to mix then is the sum of the fluid expected to enter the EV (in this example 1.5L), plus the volume held by the rest of your solar pipework/panels/coil etc.
it may also be comforting to know that you have 16.5L room for expansion in your EV!
hope this helps
first of all note that the 'EV precharge', i.e., the air pressure in the EV, which is set before the solar loop (system) is filled with fluid, should typically be set at 0.2 bar less than the system pressure you are planning (system pressure=pressure of fluid in your solar loop).
Let's say we choose a target system pressure of 1.4bar, then we should aim for an air pressure (before fluid is added) in the EV of 1.2bar. In this example we'll assume we're using an 18L EV (an EV used in a typical solar thermal installation for a normal household will generally be 12L or 18L capacity)
[1] The pre-charge air pressure is 1.2 bar+1bar = 2.2 Bar absolute
[2] The system (liquid) pressure is then raised, by filling fluid into the solar loop to 1.4bar. system pressure in absolute terms is 1.4bar +1 bar= 2.4 Bar absolute.
So the volume of gas in the EV is now (2.2/2.4) x 18 = 16.5litres
So 1.5 litres of fluid can be expected to enter the EV when filling the system, assuming the above EV precharge and system pressure settings.
when mixing up antifreeze this is a handy number to know. the total voulme of solar fluid you need to mix then is the sum of the fluid expected to enter the EV (in this example 1.5L), plus the volume held by the rest of your solar pipework/panels/coil etc.
it may also be comforting to know that you have 16.5L room for expansion in your EV!
hope this helps