tortillamuncher
Mechanical
Hi All!
I'm currently involved with a retrofit project wherein the client is insisting on the addition of various balancing valves and non return valves to the central domestic hot water calorifier system. I’m expressing some doubt because I’m not sure how effective the implementation will be because I haven’t come across such a situation before. Appreciate if someone could offer their expertise.
The application consists of:
1) 3 x 1,000 Liter SS316L domestic hot water storage calorifiers with dual energy inputs. The calorifiers are installed in the roof technical plant room.
2) Energy U-tube bundle #1 has input from a hot water boiler (80 - 60 deg C), closed circuit. Boiler circulation pump duty is 19.8 m3/hr @ 20 m head. Constant speed pump.
3) Energy U-tube bundle #2 has input from a water to water heat pump (65 - 60 deg C), closed circuit. Heat pump circulation pump duty is 22.3 m3/hr @ 20 m head. Constant speed pump.
4) The calorifier tank temp will be maintained between 55 to 60 deg C.
5) The calorifier tank has cold water inlet, hot water return, hot water supply and drain connections in addition to the energy bundles.
6) The calorifiers are fed on the inlet side by cold water booster pumps and on the outlet there is a hot water booster pump.
7) The hot water booster pumps serving the zone are designed for 40 m3/hr @ 30 m each (2-duty + 1-standby). The pumps are VFD operated.
8) The hot water return pump details are not known yet.
9) The calorifiers are piped in parallel arrangement.
10) The calorifiers are feeding hot water fixtures such as wash basins, showers, laundry, kitchen and etc…
The issues:
1) During a discussion the client raised the concern that for example if there is hot water demand how can we ensure that hot water supply is evenly distributed across all 3 tanks? Let’s say all 3 tanks are maintained at the set point temp of 60 deg C and there is a call for demand, how can we ensure all 3 calorifiers are evenly supplying the hot water as opposed to tank #1 taking priority, tank #2 supplying slightly and tank #3 remains unaffected…in peak demand there could be enough hot water stored but because the circuit is not balanced hot water only comes out from #1 which while 2 and 3 don’t contribute as much and if tank #1 doesn’t recover in time eventually only cold water/incoming feed temp will be fed to the fixtures .
To prevent such a scenario from happening he is insisting to add balancing valves to the calorifiers and to install them on the hot water outlet branch of each calorifier and also expressed a similar logic to the hot water return piping to ensure the return water is evenly distributed to all tanks as opposed to a single tank getting priority. If balancing valves are required could someone also assist on how to size...I'm not sure what to select for delta P as there is hardly any pressure drop across a calorifier tank...it's essentially one big pipe isn't it?
2) Balancing valves are also to be provided for the heat pump circuit and boiler circuit for each calorifier. I haven’t done this before but I believe I can use a fixed orifice double regulating valve and to size it should I just match the delta P of the U-tube bundle approx. 0.3 bar pressure drop and divide the design maximum flow rate by 3 for the boiler and heat pump circulation pumps? The valve will also be installed on the return / outlet of the U-tube bundle. Could I use a PICV / automatic balancing valve? Any tips for sizing?
3) To prevent temperature creep he has also insisted to place non return valves on the cold water supply, hot water return and hot water supply. The cold water supply I agree but isn’t also adding to the HWS and HWR a bit much? I haven’t seen any manufacturer’s drawings indicating NRV’s on HWR/HWS connections. He is concerned that the hot water of tank #2 could go into tank #1 hence the recommendation on the HWS as well. Similar logic for the HWR line.
I'm currently involved with a retrofit project wherein the client is insisting on the addition of various balancing valves and non return valves to the central domestic hot water calorifier system. I’m expressing some doubt because I’m not sure how effective the implementation will be because I haven’t come across such a situation before. Appreciate if someone could offer their expertise.
The application consists of:
1) 3 x 1,000 Liter SS316L domestic hot water storage calorifiers with dual energy inputs. The calorifiers are installed in the roof technical plant room.
2) Energy U-tube bundle #1 has input from a hot water boiler (80 - 60 deg C), closed circuit. Boiler circulation pump duty is 19.8 m3/hr @ 20 m head. Constant speed pump.
3) Energy U-tube bundle #2 has input from a water to water heat pump (65 - 60 deg C), closed circuit. Heat pump circulation pump duty is 22.3 m3/hr @ 20 m head. Constant speed pump.
4) The calorifier tank temp will be maintained between 55 to 60 deg C.
5) The calorifier tank has cold water inlet, hot water return, hot water supply and drain connections in addition to the energy bundles.
6) The calorifiers are fed on the inlet side by cold water booster pumps and on the outlet there is a hot water booster pump.
7) The hot water booster pumps serving the zone are designed for 40 m3/hr @ 30 m each (2-duty + 1-standby). The pumps are VFD operated.
8) The hot water return pump details are not known yet.
9) The calorifiers are piped in parallel arrangement.
10) The calorifiers are feeding hot water fixtures such as wash basins, showers, laundry, kitchen and etc…
The issues:
1) During a discussion the client raised the concern that for example if there is hot water demand how can we ensure that hot water supply is evenly distributed across all 3 tanks? Let’s say all 3 tanks are maintained at the set point temp of 60 deg C and there is a call for demand, how can we ensure all 3 calorifiers are evenly supplying the hot water as opposed to tank #1 taking priority, tank #2 supplying slightly and tank #3 remains unaffected…in peak demand there could be enough hot water stored but because the circuit is not balanced hot water only comes out from #1 which while 2 and 3 don’t contribute as much and if tank #1 doesn’t recover in time eventually only cold water/incoming feed temp will be fed to the fixtures .
To prevent such a scenario from happening he is insisting to add balancing valves to the calorifiers and to install them on the hot water outlet branch of each calorifier and also expressed a similar logic to the hot water return piping to ensure the return water is evenly distributed to all tanks as opposed to a single tank getting priority. If balancing valves are required could someone also assist on how to size...I'm not sure what to select for delta P as there is hardly any pressure drop across a calorifier tank...it's essentially one big pipe isn't it?
2) Balancing valves are also to be provided for the heat pump circuit and boiler circuit for each calorifier. I haven’t done this before but I believe I can use a fixed orifice double regulating valve and to size it should I just match the delta P of the U-tube bundle approx. 0.3 bar pressure drop and divide the design maximum flow rate by 3 for the boiler and heat pump circulation pumps? The valve will also be installed on the return / outlet of the U-tube bundle. Could I use a PICV / automatic balancing valve? Any tips for sizing?
3) To prevent temperature creep he has also insisted to place non return valves on the cold water supply, hot water return and hot water supply. The cold water supply I agree but isn’t also adding to the HWS and HWR a bit much? I haven’t seen any manufacturer’s drawings indicating NRV’s on HWR/HWS connections. He is concerned that the hot water of tank #2 could go into tank #1 hence the recommendation on the HWS as well. Similar logic for the HWR line.
