Did I hear that right

[MikeSharp01]

Just been listening to the R4 PM programme. They did a piece on Heat Pumps and one of the contributors said that Ground Source Heat Pumps (GSHP) can deliver instant hot water like a combi boiler. Did I hear that right?  

 

 

[ProDave]

You might have heard them say it, but that does not make it true.

[joe90]

My ASHP could but only because I had a DHW cylinder that stored hot water and frankly it delivered hot water faster than my current combi  boiler🤷‍♂️.

[Redbeard]

Yes, I heard that too, and have certainly never heard anything to suggest that it's true. Anyone else? 

[SteamyTea]

I missed the second half of PM.

 

Purely from a technical view point, hot needs to be defined, for any given mass flow rate.

 

Plumbing in 10, 5 kW Heat Pumps in parallel could deliver water at 45⁰C and easily at 10 kg/min.

Be a bit silly though.

 

The BBC does tend to take polarised views in heat pumps, they get a few people that can't make them work, and a few people that can make them work, forgetting about the thousands that have them that don't know, or care  how they work, but get enough hit water and space heating out if them to not have to worry.

Edited September 21, 2023 by SteamyTea

[Beelbeebub]

I guess it would be technically possible for a gshp to act as a combi if it was rated at a high enough power (18kw minimum) at 45C.

 

An ASHP couldn't do that as it needs defrost cycles every now and then. 

 

So I guess if you were to try and make a "combi" HP, effectively a box on the wall like a gas boiler, then a GSHP would be the way forward. 

 

Doesn't mean it's sensible. 

 

 

[SteamyTea]

1 hour ago, Beelbeebub said:

An ASHP couldn't do that as it needs defrost cycles every now and then. 

A GSHP would freeze the ground in the UK.  May work in a desert.

A WSHP could be made to work, but the flow rate of the ambient temperature water, or ideally sea water, would be huge to stop freezing.

Edited September 21, 2023 by SteamyTea

[Beelbeebub]

8 minutes ago, SteamyTea said:

A GSHP would freeze the ground in the UK.  May work in a desert.

A WSHP could be made to work, but the flow rate of the ambient temperature water, or ideally sea water, would be huge to stop freezing.

Depends (in both cases) on the size of the collector loop/flown rate. 

 

Specific heat of water is roughly 4kj per kg per kelvin. 

 

So 20 kW would be 1kg per second by 5k (say 10C to 5C)

 

Or 60lpm a fairly high flow but not totally impossible. 

 

But it would be a mad idea as you would be massively over sizing your system for a very nich situation. Gas boilers are very easy to oversize hence the ease of creating combis. 

 

For HPs we need to get back to (unfortunately) stored hot water. 

 

 

[SteamyTea]

3 minutes ago, Beelbeebub said:

For HPs we need to get back to (unfortunately) stored hot water. 

Energy storage is really a case of where we store it.

Can easily store thermal energy in a cylinder of water or a few bricks in a storage heater, or even in a concrete slab.

Storing gas involves disused salt caverns, highly automated processes and a lot of post processing of the raw material (gas), after it has already been processed from its place of origin.

Electricity is, currently, very expensive to store, and takes a lot of land area, pumped storage especially.

[Beelbeebub]

49 minutes ago, SteamyTea said:

Energy storage is really a case of where we store it.

Can easily store thermal energy in a cylinder of water or a few bricks in a storage heater, or even in a concrete slab.

Storing gas involves disused salt caverns, highly automated processes and a lot of post processing of the raw material (gas), after it has already been processed from its place of origin.

Electricity is, currently, very expensive to store, and takes a lot of land area, pumped storage especially.

Agreed but from a practical POV, a DHW tank is a bulky item costing about the same as a boiler with a defined capacity, which makes them a bit of a backwards for the end user vs a combi. 

 

Which is unfortunate

[ProDave]

10 minutes ago, Beelbeebub said:

Agreed but from a practical POV, a DHW tank is a bulky item costing about the same as a boiler with a defined capacity, which makes them a bit of a backwards for the end user vs a combi. 

 

Which is unfortunate

I would choose a system boiler and UVC any day over a combi boiler.  Chalk and cheese, a UVC wins hands down for pressure, flow and consistency of hot water.

[magnayn]

Our boiler can supply 42kW at 17l/min. Good luck finding a domestic heat pump that can do that!

 

1 hour ago, Beelbeebub said:

For HPs we need to get back to (unfortunately) stored hot water. 

 

 

Yeah. nah. Direct-heat, 3-phase tankless heater. Simple. Cheap. Never run out of hot water. Think big-ass electric shower.

[DanDee]

5 hours ago, MikeSharp01 said:

Just been listening to the R4 PM programme. They did a piece on Heat Pumps and one of the contributors said that Ground Source Heat Pumps (GSHP) can deliver instant hot water like a combi boiler. Did I hear that right?  

 

 

When we refer to heating instant hot water, we assume taking 10C to 50C as an example.

A flame or heating element can have hundreds degrees C

A normal HP cannot, so the only way to achieve the 50C from 10C without storage is to use two stage compressors.

There are many ways to achieve this technically, regardless of the heat source, water, air, or bean farts.

Not every GSHP is two stage, not every GSHP can do that.

 

 

 

 

Edited September 21, 2023 by DanDee

[DanDee]

3 minutes ago, magnayn said:

Our boiler can supply 42kW at 17l/min. Good luck finding a domestic heat pump that can do that!

 

 

 

Yeah. nah. Direct-heat, 3-phase tankless heater. Simple. Cheap. Never run out of hot water. Think big-ass electric shower.

why do you bother writing if you are acting like a yankee that has an army bringing home cheap oil? bring some benefit to the topic/forum discussed

[MikeSharp01]

8 hours ago, DanDee said:

A normal HP cannot, so the only way to achieve the 50C from 10C without storage is to use two stage compressors.

There are many ways to achieve this technically, regardless of the heat source, water, air, or bean farts.

Not every GSHP is two stage, not every GSHP can do that.

That's interesting - looking at the Q-Ton, details here, it seems to be able to supply only between 9 and 5 l/min, depending on season, at the temp rise and all the drawings I have found show unvented cylinders in the circuit. Still it sounds like start down the path of an instant hot water combi heat pump. 

[DanDee]

4 hours ago, MikeSharp01 said:

That's interesting - looking at the Q-Ton, details here, it seems to be able to supply only between 9 and 5 l/min, depending on season, at the temp rise and all the drawings I have found show unvented cylinders in the circuit. Still it sounds like start down the path of an instant hot water combi heat pump. 

 

Well, even if they are capable of higher instant temps, I don't see them as being sold as something to replace a combi boiler/instant heater, and in general a cylinder is still to be used as it makes more sense. 

I don't think there's a domestic HP designed specifically with that in mind, not to have a cylinder.

 

A combi get's started multiple times a day without the hot water having a change to reach the bathroom tap when tenants are washing their hands turning on the hot rather than cold water for 30seconds.

When hand washing dishes, the flow of water that gets the boiler going it's too high, such that if you deem that is too much water/hot water and try to lower it, you pause the heating of the water, thus starting the cycle of death. Old boiler that is.

 

I would want to know a HP is started multiple time more that it already does.

Edited September 22, 2023 by DanDee