In my ongoing saga, I have now fitted a grundfos ups 25-80. This is on a system with a vaillant 438, two heating zones (approx 26kw d/s, 18kw u/s), and a h/w zone. My ABV is fitted after the pump, before the 2 port zone valves.
Looking at the instructions, I have worked out that with the boiler range rated to 34kw (the heat loss on my house using the whole house method), my boiler needs a minimum flow of 1462l/h. The 25-80 provides 6.75m head at that flow rate, and the honeywell du144 instructions show a setting of just below 0.2 bar (1.75 on the dial).
Now my understanding is that with the whole system running, the bypass should not be open. As TRV's shut down, the bypass begins to open to maintain minimum flow. This seems to work as expected - however, as my heating is divided into two zones, effectively, half the system is closed with only one zone in operation. This means the bypass is open even under normal operation. This does not seem to impact the ability for the rads to get hot, but I'm wondering if a) this is how it should be set on a two zone system, and b) is this wasting energy?
Thanks.
Looking at the instructions, I have worked out that with the boiler range rated to 34kw (the heat loss on my house using the whole house method), my boiler needs a minimum flow of 1462l/h. The 25-80 provides 6.75m head at that flow rate, and the honeywell du144 instructions show a setting of just below 0.2 bar (1.75 on the dial).
Now my understanding is that with the whole system running, the bypass should not be open. As TRV's shut down, the bypass begins to open to maintain minimum flow. This seems to work as expected - however, as my heating is divided into two zones, effectively, half the system is closed with only one zone in operation. This means the bypass is open even under normal operation. This does not seem to impact the ability for the rads to get hot, but I'm wondering if a) this is how it should be set on a two zone system, and b) is this wasting energy?
Thanks.
