Water source heat pump, - COP 13 April 2022 at 5:53PM in Green & ethical MoneySaving 10 replies 111 views

waqasahmed

Just wondering if these are worth it? They apparently have a higher COP than ASHPs and don't cost much more. Also if anyone knows what you would expect over a year for COP on WSHPs? 

I wonder then why ASHPs are being pushed instead. Is it due to them being more reliable? 

Martyn1981

It actually could be a really important source of space heating for large companies, or even district heating, since in the UK, most large towns and cities are port based, or have a large river running through them (near them). And you can even co-locate space heating with cooling of data centres by sharing a water source, without actually having to transfer the heat/cold between them directly.

I think some of the very large buildings on the island of Manhattan use WSHP for heating/cooling.

But of course, you'll need a large volume / source of water, which on an individual home basis may be a problem.

Some years back there was a Grand Designs episode being built next to an old water mill and mill pond, actually the mill pond was really a small lake. Got me thinking that a small hydro generator could be used to demand follow, and the smaller 'after' pond would be ideal for WSHP, since in the winter when PV is low, you'd probably be running the hydro, to power the HP, and thus flushing out the water faster than it's being cooled.

QrizB

Do you have a lake or river in your garden? Do you live on a houseboat, or have a moat?

waqasahmed

QrizB said:

Do you have a lake or river in your garden? Do you live on a houseboat, or have a moat?

Ahhh so it can't just pull that water from a tap

Martyn1981

BTW under the heading of when life gives you lemons, here's a pick of something interesting I saw years ago on another site.

So, part of your driveway collapses, and you find you have a very old, small, culverted water course under your property, what do you do? You repair everything, make an access route, and repair the culvert in such a way as to form a small pool, then you build your own WSHP ..... of course!

QrizB

waqasahmed said:

QrizB said:

Do you have a lake or river in your garden? Do you live on a houseboat, or have a moat?

Ahhh so it can't just pull that water from a tap

Sadly, no.

Although ...

Let's assume it's winter, your incoming mains water is at 6C and you're happy to chill it to ever so slightly above 0C.

Each cubic metre of water will supply you with 6 x 4.2 x 10^6 Joules, 25.2 MJ, which is 7 kWh.

I don't know what you pay for your mains water but mine is metered at around £2/cu.m., so roughly 28p/kWh. That's the same price as direct electric heating just for the water without considering the cost of the electricity to run the heat pump!

Reed_Richards

Worst case ever for my heat pump is about 50 kWh used in a day.  So that would require a bit more than 7 cubic meters of water used in a day, 7000 litres in 1440 minutes or something like 5 litres per minute.which is what you could achieve from an ordinary tap.  So I have the cold tap running, I wonder how much surface area I need to chill the water down by 6 C?  Because there is actually a stream that runs along the edge of my garden so I could do better than running a cold tap.  Tends to slow to a trickle in summer though.   

Meatballs

waqasahmed said:

QrizB said:

Do you have a lake or river in your garden? Do you live on a houseboat, or have a moat?

Ahhh so it can't just pull that water from a tap

Can't tell if this is genius sarcastic reply directed at yourself or not 🤣

Screwdriva

QrizB said:

Do you have a lake or river in your garden? Do you live on a houseboat, or have a moat?

We do. I'm intrigued. Any thoughts on the area requirements for the coils? 

Reed_Richards

It must depend on how fast the water is flowing.  If you have to rely on convection to remove the chilled water it will be less efficient than if there is a current so you would need a lager area of coils.  I suppose you might be able to use a propeller as the underwater equivalent of the fan in an ASHP but then that's more electrical energy required.

gefnew

This may help.
A guide to water source heat pumps - Energy Saving Trust