Posted by: @mattc

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Posted by: @hughf

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Avoid midea…. It will come from freedom and be fitted with a LLH or PHX that will cripple the efficiency.

That's a shame.  I was beginning to veer towards Midea. What's the issue with freedom/LLH/PHX?  I obviously need to do some more research, but could you provide a quick summary?

Thanks

 

 

LLH - low loss header, basically some kind of buffer tank, I don't know the details. 

PHX = plate heat exchanged, which in your water tank or buffer will lose you energy compared to better heat exchangers. 

Both of these are just a way to provide hydraulic separation between the heat generator and the emitter circuit. It wouldn't matter if we weren't living in a country with the largest ratio between electric and gas costs. That means we're chasing every ounce of efficiency.

Heat pumps are always advertised against direct electric heating (in foreign lands, where most of them are manufactured), and in that case they are always cheaper to run. When comparing against gas, you need to chase every ounce of efficiency, and that means avoiding hydraulic separation.

Hydraulic separation makes it very easy to install without there being any risk of low flow errors causing an issue. Heat pumps delivers heat at whatever flow it wants into the buffer/LLH/PHX, and the heating circuit can pump from the other side of this separation at whatever flow rate the radiators/pipework limit you to.

On the topic of low loss headers and PHX, I did a search online and found this blog post thing by a Grant person,

https://www.grantuk.com/about/blog/the-case-for-the-low-loss-header/

Having a scan through, it seems to me that their opinion makes sense if you don't bother designing and building the system carefully and just whack it in instead of a boiler...

Thanks.  That's helpful.  Learning slowly.

Posted by: @guthrie

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On the topic of low loss headers and PHX, I did a search online and found this blog post thing by a Grant person,

https://www.grantuk.com/about/blog/the-case-for-the-low-loss-header/

Having a scan through, it seems to me that their opinion makes sense if you don't bother designing and building the system carefully and just whack it in instead of a boiler...

As I said (or at least I think I said, perhaps I said it on buildhub), it only matters as we are chasing efficiency numbers because we need to compete with gas. In countries where the alternative is direct electric heating, if your heat pump runs at a cop of 2.5, it matter a lot less.

When we see the levies moved off electric and added onto gas, then it won't matter and we can easily install more heat pumps without needing system redesign/rework.

The major drawback with that philosophy, is there will then be the need for more electrical energy generation and transmission, which in turn will increase the amount of electricity supply infrastructure improvements that will be require. Guess who will have to pay for all those improvements?

If everyone concentrates upon reducing energy consumption, then that will help reduce the costs for everyone.

@derek-m Indeed.... insulate britain had the right idea, but just went about getting the message across in the worst way possible...

Returning to the LLH/PHX question, would it be fair to say that these things essentially trade performance (efficiency) for robustness? 

I guess if a large number of end-users just want a set-and-forget system, or don't have the capacity to monitor and fine-tune themselves, then this might be a reasonable approach, depending on the relative cost/benefits.

EPC inspection happened this morning (£60, 30 mins). Waiting with baited breath for results.

Posted by: @mattc

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Returning to the LLH/PHX question, would it be fair to say that these things essentially trade performance (efficiency) for robustness? 

I guess if a large number of end-users just want a set-and-forget system, or don't have the capacity to monitor and fine-tune themselves, then this might be a reasonable approach, depending on the relative cost/benefits.

EPC inspection happened this morning (£60, 30 mins). Waiting with baited breath for results.

Buffer tanks, LLH's and PHE's were required in systems using gas or oil boilers, where radiators would be fitted with TRV's, or in zoned systems where zone valves could be opening and closing.

When any of the above items are used within an ASHP heating system, they not only make the system operation more difficult to balance, but also can dramatically reduce overall operating efficiency. They should therefore be avoided if at all possible.

It is the responsibility of the installer to provide the customer with a correctly operating heating system, that is not using more electrical energy than is reasonably required. Allowing installers to include any of the above items, merely allows the installer to provide a system that works, but removes the necessity for the installer to have to correctly optimise the system operation.

It is like selling a person a car, but insisting that they drive everywhere with the engine revving above 5000rpm. It gets the car user from A to B, but I suspect the fuel economy will be far from ideal.

Got it. Thanks

EPC results are in.  We got a 73 (C) with recommendations for additional floor insulation and solar.  Nothing on wall or loft insulation, so it looks like we're good to go.

Returning to the question of the Mixergy cylinder, I found this article helpful.

https://energy-stats.uk/mixergy-heat-pump-performance/

I had previously been told that I would need to get the 'heat pump kit' with the Mixergy cylinder, which appears to be a PHX.  According to the article, this is needed because the coil in the indirect version of the Mixergy is too small for use with a heat pump.  Given this information (and this forum's aversion to PHX's) I'm probably going to drop the Mixergy idea and go with a conventional indirect cylinder.

Any other comments?