@iaack of course, you're right, but that's not the market the OEM of 'Heat Saviour' is targeting, They are targeting retrofit ASHP heat pump market, so it clearly says in their marketing literature. I can't see this product offers any advantages to that market, save purely the convenience of the retrofit installer. The home-owner or occupier is the party disadvantaged, with a built-in thermodynamic inefficiency and additional running cost of a second circulator pump that in many smaller homes would not be needed.

Sadly we don't really do district heating in the UK to any great extent. Shame, as larger air, ground or water source heat pumps serving multiple dwellings offer efficiency advantages. Most houses have their own CH and DHW fired combustion combi boiler. If the UK is committed to replacing those in pursuit of Net Zero 2050 and to decarbonise domestic heating, then replacement products should compliment best practise and best efficiency. 'Heat Saviour' doesn't, it lowers the SCOP potential of the ASHP by adding a 2nd PHX in the design in addition to the one in the heat pump. It increases running costs, by requiring a second circulator, and by raising the design LWT temperature on the primary circuit side to achieve the required flow temperature on the secondary side.

@allyfish As you say, all the ‘plus points’ and ‘advantages’ are very much for the benefit of the installers - the costs to the end user would appear to be irrelevant! It really is a shame that the advertising / sales fraternity have such finely tuned aims (that rarely if ever extend to providing any advantage to the end user!).☹️ Toodles.

I happen to have a Heat Saviour (HS)in my system!

After nearly 4 years I have quite a lot of daily data on both electric usage and outside temperature. 

Observations on discussion so far:

- claims that plates are thermodynamic ally inefficient whereas web suggests that they are highly efficient

- claims that they are for the benefit of the installer only.

This interesting explanation

https://savree.com/en/encyclopedia/plate-heat-exchanger-phe

says they are highly efficient generally but work best in a contraflow configuration and adherence to the principle that hotter water rises and therefore the hotter fluid (either flow or return) should be at the top. As best I can tell the HS runs the plates horizontal. I do not know if it has a chevron plate design. The aim is create turbulence to make effective use of the full area of each plate.

Regarding efficiency there are two issues:

- heat lost through the external surface, which is actually quite small 

- does it allow the ASHP to achieve a delta of 5C and likewise the rads

My observations of my system are

- that ASHP side is 4C and the Rads 3C measured continuously close to the HS

- Hewers installed it with parallel flow and have not changed this or justified their way being right. I can’t but help feel the delta would be improved but the HS design seems inherently to be wrong if indeed the plates are horizontal.

In use I have dropped the ASHP flow to 35c and built and installed a housing below every rad to force air driven by a fan in the housing through the rads rather than relying on convection. It has been a noticeable improvement. So far in January I have only used 530kWh. At -6C I used 41 kWh (24h average-1.6C). More recently about 10-17kWh. All this for a very large 300m2 property with EPC of C. On Intelligent GO it is cheap to run given I have battery and solar.

@filipe  Im not absolutely sure from your post whether you are pleased on not with your installation but get the impression you are in which case thats good to hear.

Plate heat exchangers in contraflow configuration are indeed pretty efficient.  Nevertheless there must always be a temperature drop across them (between primary and secondary) which be compensated for by increasing the flow temperature from the heat pump, thus reducing its COP.

The key question with this piece of kit is no, does the system work with it, its would it work without it?  Put another way, what problem is it solving for the householder that justifies the expense of the kit  and extra water pump, the cost of installation and the probable reduction in efficiency due to the temperature drop? 

In almost all cases the answer is that it isn't solving a problem or at most isn't solving a problem that couldn't be better solved another way.  Just like a buffer tank its almost certainly unnecessary, certainly costs money, and very probably compromises performance.  The way its sold targets it at social housing, the occupants of which presumably don't have money to throw away, and the floor area of which is unlikely to be anywhere near that where plumbing arrangements more complex than simply connecting the heat pumps to the emitters might be necessary.

Hence the criticism.  However if you have it and you are happy that's great, but of course it doesn't prove you wouldn't be equally happy without.

@jamespa 

I should have mentioned my flow temperature is fixed at 35C which you can see in the photo. I quite agree about contraflow but have failed to get the installer to do anything. The secondary pump uses about 20W compared to the ASHP’s 1.5kW in heating mode. It ran continuously for more than 6 hours today. On the day in the photo it cost me £1 to heat the house - about 15kWh for 300m2 floor area and 6 large bedrooms etc. So it does alright.

• So how can I get the installer to take action under MCS?
• I’m hoping the contraflow gives a better delta T and that I can run the ASHP harder unless I need more plate 

Thanks Phil

Posted by: @filipe

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So how can I get the installer to take action under MCS?

You probably cant, MCS is, at least from the reputation it has here,essentially useless as a consumer protection organisation

Posted by: @filipe

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• I’m hoping the contraflow gives a better delta T and that I can run the ASHP harder unless I need more plate 

 

Contraflow should reduce the difference between the flow temp from the heat pump and flow temp to emitters, which means you can reduce the former improving COP.  It wont make the heat pump work harder nor is there a reason to do so. 

There is nothing wrong with your current DT of 3/4 so dont worry about this!

Overall I get the impression your system is working pretty satisfactorily so perhaps dont change anything!  Is there an actual problem you are trying to solve?