I recently paid British Gas to replace my old boiler with a new condensing one. My question concerns how to get the maximum efficiency from the new boiler when heating only the hot water.
My house is a four bedroom, two story detached. The new boiler is a Worcester Greenstar 24Ri. It is an open vented fully pumped system with 13 radiators that are mostly doubles and a 3-port diverter valve. The pump is a Grundfos UPS15-60 Super Selectric.
With my old boiler, the pump was set to speed 2. To achieve 20°c drop across the new boiler I have reduced the speed to setting 1. The central heating now takes longer to heat the house but the 20°c drop across the boiler is maintained for most of the heating cycle. I have measured this with radiator thermometers clipped to the flow and return above the boiler. However, when heating hot water only, the flow and return temperatures are very close, typically 70°c flow 65°c return, so the return temperature is above the condensing level. The boiler cycles on and off until the cylinder stat switches off. The boiler gas valve modulates correctly.
My question is, would there be any gain in efficiency by fitting an in-line balance valve in series with the hot water cylinder coil and adjusting it to reduce the rate of flow and therefore the return temperature during hot water heating. Would this achieve the aim of forcing the boiler into condensing mode during hot water heating, thus reducing my gas bill?
Andy Miles
My house is a four bedroom, two story detached. The new boiler is a Worcester Greenstar 24Ri. It is an open vented fully pumped system with 13 radiators that are mostly doubles and a 3-port diverter valve. The pump is a Grundfos UPS15-60 Super Selectric.
With my old boiler, the pump was set to speed 2. To achieve 20°c drop across the new boiler I have reduced the speed to setting 1. The central heating now takes longer to heat the house but the 20°c drop across the boiler is maintained for most of the heating cycle. I have measured this with radiator thermometers clipped to the flow and return above the boiler. However, when heating hot water only, the flow and return temperatures are very close, typically 70°c flow 65°c return, so the return temperature is above the condensing level. The boiler cycles on and off until the cylinder stat switches off. The boiler gas valve modulates correctly.
My question is, would there be any gain in efficiency by fitting an in-line balance valve in series with the hot water cylinder coil and adjusting it to reduce the rate of flow and therefore the return temperature during hot water heating. Would this achieve the aim of forcing the boiler into condensing mode during hot water heating, thus reducing my gas bill?
Andy Miles