Wednesday, April 28, 2010

Pumpflow questions: C Wood

28 April : Had an interesting discussion with Dr Chris Wood in the Uni.  The main topic was about pump flow.
  He praised the decision to put a 3-port solenoid valve (Danfoss) to divert ALL the glycol to the sunboxes when the thermostat commands, because it will make it far easier to identify the contribution made by the sunboxes. I said that if it drained as much heat as was available more efficiently, the pump in the loft would be turned off by the thermostat until the sunbox air temperature increased naturally.
  He did question whether the pump in the loft should be running when the GSHP is on. At the moment it is necessary to divert a fraction of the glycol to the sunboxes, while the other fraction goes down below. The loft pump is absolutely necessary for pumping heat down to the ground when the GSHP is dormant for long hours of the summer. But what about when it is working?
   Once we have the 3-port valve, all glycol goes up to the sunboxes. The loft pump is merely speeding up the flow sent to the sunboxes, and would this be too fast? Do we need the 'parasitic energy consumption' of the extra pump if it is not helping the process? Would it be better to have it turn off when the heatpump's water pump comes on? (and would this be a restriction on the flow?) More importantly, does it confuse the algorithm inside the GSHP controller which expects glycol to move at one speed when (unknown to it) the glycol is arriving faster than expected? I am hoping it is smart enough to recognise the watt-hours moving towards it, and adapt accordingly. The GSHP has a manually settable variable speed glycol pump (set to highest speed). The GSHpump just seems to work for fewer hours or minutes if the heat coming in is good for its needs.
  In the same vein, do we really need the external supplementary pump for the underfloor circuit? Does this confuse the controller, or cause too much circulation? I can disable the external underfloor heating pump.
  The Danfoss is now in stock just near the University campus, so I will try to collect it today.

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