Sunday, October 3, 2010

'Trickle' and 'Whoosh' explained

3 Oct '10: I have added more to the Glossary, as people here and on the Navitron forum are asking more questions about the system design, especially the plumbing. So, what do I mean by Trickle and Whoosh?

'Trickle' = Circulating glycol through the Sunboxes at about 5 litres/minute using the low power consumption pump in the loft.
'Whoosh' = Circulating glycol through the Sunboxes at about 18 litres/minute using the circulating pump in the heat pump. This only occurs when the heat pump is doing a heating cycle for DHW or Underfloor Heating.

'Trickle-and-Whoosh' = Plumbing arrangement with a 3 port solenoid valve so that when the Thermostat says Yes! the entire ground loop is diverted sequentially through the Sunboxes at 'whoosh'-speed, downloading any heat very quickly, chilling the sunboxes quickly, and then the thermostat says No!, allowing the valve to close again, and turn off the loft pump. It reduces pump power consumption. This is only possible if the pipe sizes are large and the black collectors support fast flow. Over the length of a day, the difference in total thermal capture is likely to be similar to Trickle while we Work, but collected in intermittent pulses. This is what we use on the Peveril Solar House. If 'Whoosh' occurs, it just pushes through the 'Trickle' pump.

'Trickle-while-we-Work' = Plumbing arrangement so that the loop through the Sunboxes is a parallel bypass to the existing ground loop, working at 5 litres/min and is controlled by a 2 port solenoid valve. This circulates whenever the thermostat says Yes!. When the heat pump is running a heating cycle, the Sunbox loop merely injects (dilutes) the warmer fluid at 5 litre/min into the fast flow, meaning that the thermostat sees a favourable delta-T for far longer, saying Yes! for 3 or 4 times longer perhaps. A non-return valve is required to make sure that the circulation goes in the right direction. This enables one to use narrower pipes and narrow diameter metal collectors, but will cause longer hours of pump consumption. This is what we will use on the East Leake house.

This T-w-w-W method is not so effective. Trickle while we Work will inject the heat into the circuit, but being diluted it is not going to catalyse the GHSP, it just contributes helpfully. With the Trickle and Whoosh system, the ground loop gets a larger amount of liquid coming down, sometimes at above the normal ground temperature, thus lining the earth around the pipes with greater than average warmth - a temporary and welcome uplift.

The main difference between using these Sunboxes and industry standard solar panels is that we don't need an intermediate tank. Those solar panels are very well insulated, so do not pick up anything significant from the air temperature, although they will get warmth from a bright sky. With an insulated backing, they do not have any thermal capacity of their own.

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