GSHP, loops in a lake.

[Jeremy Harris]

39 minutes ago, SteamyTea said:

Yes, but I am sure all this has been sorted out already.

There are a few boats that have heat pumps fitted, they have the same problems.  The marine industry may be the place to look.

 

 

The pumping energy problem is non-trivial, though, as it's just down to the energy needed to move a large volume of water.  That reduces the effective COP to less than that for a very much cheaper ASHP, so it becomes pointless to use an open water collector system in the majority of cases.  A boat can get away with using dual purpose pumps, by using engine cooling heat exchanger water, so the additional pumping demand is reduced, but most domestic systems will need to lift the water up by a couple of metres or so, more for a standing column collector.

 

The volume of water needed is also high, above the 20,000 litre per day limit for licence-free abstraction (and an open loop heat pump is classified as abstraction, even though the water goes straight back from where it came).  I was looking at lifting the water around 5 to 6 metres from a standing column system, using a small Kensa heat pump.  That would have needed a 600 W pump to be able to deliver the required volume flow through the heat pump, and the effective COP would have reduced from well over 4 to below 3 as a consequence.  A closed loop collector system would have reduced the pumping power a lot, down to less than 50 W.

 

When it comes to filtering, then I agree, the semi-self cleaning filters used on ships could probably be down-sized and made affordable for use with a water source heat pump.  I've not seen any smaller versions of these through, and the strainers on small boat sea cocks tend to clog even with a moderate water throughput.

 

 

[SteamyTea]

I think Kensa made some systems for the RNLI, they would have been small.

Also you don't have to lift water that high, though that does depend on where the system is in relation to the lake and the house.

Generally the CoP of a water source system is much higher, 4 or 5, so that should negate losses.

[scottishjohn]

this small man made island  makes me think lake is shallow .

how deep is lake ?

how often does it get ice on it in winter?

If so then  freezing   needs to be considered 

pipe would need to be very well distributed  across whole of lake so you don,t get the freezing  @JSHarris  reported .

the more we discuss it the more a ASHP looks  like it could be cheaper depending on heat load of house.?

start with that ,then work out how much piping you need to get a low temp drop in water from gshp ?

could be that overall the average temp of water is much lower than average air temp year round ,so any increase in COP might be wiped out  by lower water temp?

do you know other man that has GSHP from lake --  ask lots of questions of him  and then if he and others are sucking heat from lake is there enough left for you ?

a very knotty problem  to get a definite answer to 

 and then there is sepa   -I was told in scotland i would need SEPA to approve it as i might be freezing the bugs in the lake  

 

Edited May 9, 2019 by scottishjohn

[Ed Davies]

Can't an open-loop system operate on a circulating pump by treating the loop as a syphon? Obviously not over 10 metres but for a metre or two above a lake that should be easy enough to set up, I'd think. Might have to periodically pump air out of the top of the loop but that shouldn't be a problem - automatic air vent at the top with a valve to close off the outlet side.

[Russell griffiths]

On 09/05/2019 at 09:02, scottishjohn said:

this small man made island  makes me think lake is shallow .

how deep is lake ?

how often does it get ice on it in winter?

If so then  freezing   needs to be considered 

pipe would need to be very well distributed  across whole of lake so you don,t get the freezing  @JSHarris  reported .

the more we discuss it the more a ASHP looks  like it could be cheaper depending on heat load of house.?

start with that ,then work out how much piping you need to get a low temp drop in water from gshp ?

could be that overall the average temp of water is much lower than average air temp year round ,so any increase in COP might be wiped out  by lower water temp?

do you know other man that has GSHP from lake --  ask lots of questions of him  and then if he and others are sucking heat from lake is there enough left for you ?

a very knotty problem  to get a definite answer to 

 and then there is sepa   -I was told in scotland i would need SEPA to approve it as i might be freezing the bugs in the lake  

 

Lake is between 5-7 foot, 

lake is all ours, neighbour has his own lake,

i know the neighbour very well and he loves his system, but it has been in a while and he gets a large fit payment that covers energy usage, so his view maybe a bit lopsided. 

[Jeremy Harris]

2 hours ago, Russell griffiths said:

Lake is between 5-7 foot, 

lake is all ours, neighbour has his own lake,

i know the neighbour very well and he loves his system, but it has been in a while and he gets a large fit payment that covers energy usage, so his view maybe a bit lopsided. 

 

As you know, we're pretty familiar with the GSHP systems that Anthony has installed.  I'd have to say that they are far from being optimal, and he has made expensive changes to them as a consequence of feedback from guests.  We didn't complain about the loud noise from the GSHP, but I gather that other guests had, as Anthony spent a lot of money relocating the heat pumps from inside the cabins to outside, which did make a modest reduction in the noise level.  It still wasn't quiet, though, nowhere near as quiet as our ASHP.  The area there is pretty quiet, though, which makes any noise more noticeable.