Thursday, April 28, 2011

Time around the circuit

27 April '11: Watching the summer time circulation, I can see the temperature going down, and the temperature of the returning liquid. So that should give another indication of how much heat is deposited in the ground. 

 I just calculated the volume of liquid in the loop from the Heat pump into the ground (not counting the loop that goes through the panels) It's a pity we can't do a sort of Pooh Sticks method to find out how long the glycol takes to get round.
Upper: When I had to fill the upper system it required 20 litres of neat glycol and 40 litres of water, that is 60 litres in total. (I had a 20 litre container for pouring, so know this precisely)
Lower: For the lower loop, we have near-enough 200 metres combined length and a 40mm pipe all the way round, whose internal diameter is 32mm, which has a cross sectional area of 0.0008 m2, which gives an internal pipe volume of 160 litres.
 Total: This makes 220 litres total for both parts of the loop.

As the slow pump speed is 300 litres/hour (5 litres a minute), it must take about 44 mins for one entire circulation to take place at the slower pump speed. (When the GHSP is running, it goes at 18 litres/minute, more than 3 times that speed).
The temp diff between going down and returning is about 2.5 - 3.5 degs C.

With specific heat of the liquid of 4.0 kJ/kgK, that suggests: 4 x 300 x 3.5 *1000 / 3600 

That is equivalent to 1.17 kilowatt - i.e. in one hour, just over 1 kilowatt hour of heat deposited. As the data from the energy meter confirms a figure close to that, then I am glad to find agreement. 1.17 kW is almost exactly the average capture we got throughout last Summer.
I have long noticed that during the Equinox and Winter when the GSHP is running and forcing down the loop temperature, the delta-T improves and the rate moves up to 1.5 or even 2.0.

No comments:

Post a Comment

Comments will be moderated before showing. Please make them relevant to the subject of the posting. Comments which advertise commercial products will usually be deleted.

Popular Posts

There was an error in this gadget