Sorry for not coming back - I completely forgot about your problem over the Easter weekend. 1. From the 38 HXi pressure loss graph (attached) we know that, at full output, the flow is 1.633m³/hr and the pressure loss is 4.05m. 2. From the UPS 25-80 graph (attached)we know that, on speed 3, a flow of 1.63m³/hr produces a head of 6.75m. 3. This means that the radiator circuit is producing a loss of 6.75 - 4.05 - 2.7m 4. We have already ascertained that the heat loss is only 28kW so the required flow is only 1.21m³/hr 5. This means that the radiator loss reduces to 1.48m (loss is proportional to flow squared) 6. The head loss of a CDi heat exchanger (attached)at 1.21m³/hr is approximately 1.6m. (Green line) 7. The total head loss is therefore 1.48 + 1.6 = 3.08m 8. The Alpha1 15-50/60 will provide a flow of 1.41m³/hr with a head of 4.22m (Alpha1 graph attached) 9. A flow of 1.41m³/hr will produce a temperature differential of about 17C. 10. The Alpha1 15-50/60 consumes about 35W
I forgot to add that if the UPS 25-80 is retained it could be set to speed 2 giving a flow rate of 1.63m³/hr and a head of 5.58m. The power consumption would be about 120W. The flow rate is equivalent to a temperature differential of about 15C.