Heating source for DHW

[Archer]

Working through ideas for our retrofit and looking for advice on whether there are any benefits in keeping the heat source for the heating and hot water separate...? 

 

Here's my thinking - we currently have an old gas fired warm air heating system which is coming out; we have a newer vented hot water cylinder heated by a solar assisted heat pump ("thermodynamic panel"). The question is whether we leave this in when we update the system - because it's only 6 years old and cost the old owner c.£7k to install - or whether we just put everything through the new ASHP we are planning on installing. 

 

In my mind, if we left it then it should mean a cheaper/ simpler install for the heating system, needing a smaller ASHP. Also, are some of the installation problem people experience due to the added complexity of running heat and hot water concurrently - with different flow temperatures etc? Maybe I've got this wrong...? 

 

The downside with leaving it are that the SAHP "Magic Box" we have was installed by a company that are no longer trading. There's very little uk information about these systems generally and my concern is what we do to get it serviced or when it breaks completely. If it costs another £7k to replace it would be ridiculous. 

 

Sort of leaning towards leaving it in with the option of fitting a combined hot water cylinder/heat pump in the future. I didn't even know these existed until stumbling across them on this forum! 

 

Any advice or thoughts welcomed. 

Cheers. 

[Archer]

As an aside to my post above... We got our smart meter home energy display fitted today - so I can start to have a play about with the SAHP to see what real world efficiencies it is achieving with our hot water. There seems to be scant information online about this so I guess it might be useful for others. Will put something up when I have a chance. 

[JamesPa]

48 minutes ago, Archer said:

Working through ideas for our retrofit and looking for advice on whether there are any benefits in keeping the heat source for the heating and hot water separate...? 

 

Here's my thinking - we currently have an old gas fired warm air heating system which is coming out; we have a newer vented hot water cylinder heated by a solar assisted heat pump ("thermodynamic panel"). The question is whether we leave this in when we update the system - because it's only 6 years old and cost the old owner c.£7k to install - or whether we just put everything through the new ASHP we are planning on installing. 

 

In my mind, if we left it then it should mean a cheaper/ simpler install for the heating system, needing a smaller ASHP. Also, are some of the installation problem people experience due to the added complexity of running heat and hot water concurrently - with different flow temperatures etc? Maybe I've got this wrong...? 

 

The downside with leaving it are that the SAHP "Magic Box" we have was installed by a company that are no longer trading. There's very little uk information about these systems generally and my concern is what we do to get it serviced or when it breaks completely. If it costs another £7k to replace it would be ridiculous. 

 

Sort of leaning towards leaving it in with the option of fitting a combined hot water cylinder/heat pump in the future. I didn't even know these existed until stumbling across them on this forum! 

 

Any advice or thoughts welcomed. 

Cheers. 

Assuming you need MCS you will likely be limited by what the installers will agree to, see (many) other discussions on this forum.  The MCS rules come close to requiring a replacement (they don't actually go that far, but they come fairly close) and many MCS installers, particularly in the South East, want to fit pre-plumbed cylinders provided by the HP system manufacturer, because its dead simple.

 

DHW and Heating do not run concurrently, its either/or.

 

Opinions will differ on whether replacing DHW is necessary/a good idea/silly.  In your case I imagine that you get solar heating of your DHW for half the year or more and losing this seems like a bad deal, but as I say you might not have a choice and of course if you are concerned about reliability then submitting to general view that a new unvented cylinder with a big coil (3sq m) is the way to go that may be enough to persuade you.

 

Others may well comment in a more opinionated fashion, personally I would recommend reading a few related threads and forming your own ideas of the trade-offs (feel free to test them here but be warned some have very strong opinions).  I would also recommend not being too committed to any particular solution if you need MCS, because you will quite likely not get the option!

 

Apologies if this wasn't the definitive answer you were hoping for.

[ReedRichards]

58 minutes ago, Archer said:

...we have a newer vented hot water cylinder...

 

Water pressure good enough?  Does the shower require fine-tuning to get the right temperature?  If you answered "no" to the first question and/or "yes" to the second than you have a case for getting an unvented cylinder.

[Archer]

58 minutes ago, JamesPa said:

Assuming you need MCS you will likely be limited by what the installers will agree to, see (many) other discussions on this forum.  The MCS rules come close to requiring a replacement (they don't actually go that far, but they come fairly close) and many MCS installers, particularly in the South East, want to fit pre-plumbed cylinders provided by the HP system manufacturer, because its dead simple.

 

DHW and Heating do not run concurrently, its either/or.

 

Opinions will differ on whether replacing DHW is necessary/a good idea/silly.  In your case I imagine that you get solar heating of your DHW for half the year or more and losing this seems like a bad deal, but as I say you might not have a choice and of course if you are concerned about reliability then submitting to general view that a new unvented cylinder with a big coil (3sq m) is the way to go that may be enough to persuade you.

 

Others may well comment in a more opinionated fashion, personally I would recommend reading a few related threads and forming your own ideas of the trade-offs (feel free to test them here but be warned some have very strong opinions).  I would also recommend not being too committed to any particular solution if you need MCS, because you will quite likely not get the option!

 

Apologies if this wasn't the definitive answer you were hoping for.

Very useful post, thank you. 

 

Your last point seems to be absolutely my experience based on a couple of conversations. I've just spoken to a great MCS engineer who has installed the same SAHP system that I have - he was pretty positive about them actually, says that they give good efficiencies and rarely break because of their relative simplicity. He was comfortable either keeping the existing or replacing with something new - said that either option was fine and that he could do repairs on it as well because the manufacturer is more trading under a new name. Bonus! 

 

I was a bit surprised that he was unable to install a reversible ASHP under the Boiler Upgrade Scheme though (ie. for cooling). Is that everyone else's experience as well (and sorry if it's been covered elsewhere)?

[Archer]

59 minutes ago, ReedRichards said:

 

Water pressure good enough?  Does the shower require fine-tuning to get the right temperature?  If you answered "no" to the first question and/or "yes" to the second than you have a case for getting an unvented cylinder.

We probably need to get it properly tested. We have a cold water tank in the loft at the moment so shower pressure is driven by that and seems acceptable but not amazing. Temperature has been ok but it would be nice to get rid of the pumps etc

[JamesPa]

30 minutes ago, Archer said:

I was a bit surprised that he was unable to install a reversible ASHP under the Boiler Upgrade Scheme though (ie. for cooling). Is that everyone else's experience as well (and sorry if it's been covered elsewhere)?

So far as I know they are all reversible because that's how they do defrost.  Vaillant require a 'key' to operate in cooling mode, costing £200, it's a 5,p resistor in a 20p plastic case, others may have an installer setting disabling cooling mode.

 

But cooling is not just about the hp, the emitter and distribution system needs to be suitable too.  I don't think the government wants to or should encourage the routine use of Aircon hence the BUS conditions.

Edited May 12, 2023 by JamesPa

[Archer]

I think you're absolutely right that the govt wishes to discourage installations for use as aircon but I feel it's a slightly outdated view on the debate - as the grid decarbonises rapidly there is less and less of an issue around emissions - and this can be further offset with rooftop PV where appropriate. 

 

Conversely, the situation we have now are big challenges preventing widespread adoption of heat-pumps, especially cost but also familiarity, aesthetic, complexity etc. IMO the govt should encourage anything that supports adoption as part of the bigger picture and cooling modes are a unique selling point against boilers, and will become more so over time with global warming. 

[ReedRichards]

15 hours ago, JamesPa said:

But cooling is not just about the hp, the emitter and distribution system needs to be suitable too.

Condensation is a potential bugbear; you don't want pools of water under each radiator.  I'm not sure if radiators convect so effectively in reverse; I've seen it suggested that they don't. 

[eniacs]

15 hours ago, Archer said:

I think you're absolutely right that the govt wishes to discourage installations for use as aircon but I feel it's a slightly outdated view on the debate - as the grid decarbonises rapidly there is less and less of an issue around emissions - and this can be further offset with rooftop PV where appropriate. 

 

Conversely, the situation we have now are big challenges preventing widespread adoption of heat-pumps, especially cost but also familiarity, aesthetic, complexity etc. IMO the govt should encourage anything that supports adoption as part of the bigger picture and cooling modes are a unique selling point against boilers, and will become more so over time with global warming. 

 

Exactly this, with masses of insulation in a house suitable for ASHP's summer overheating is likely.

 

I am building my system around cooling being used 50% of the year and am frustrated by the lack of cooling on the BUS so have just bought my own direct.

 

I suspected the government have stipulated this to prevent the BUS being used to install cooling systems that never get used to heat. 

[JamesPa]

2 hours ago, ReedRichards said:

Condensation is a potential bugbear; you don't want pools of water under each radiator.  I'm not sure if radiators convect so effectively in reverse; I've seen it suggested that they don't. 

A couple of the fancoil companies advertise 'light cooling' mode, basically keep the flow temp above the dew point and lightly blow air over the radiator.  It's entirely plausible that this is sufficient to make a difference in the UK climate and could be done by adding accessory fans to ordinary radiators.  

[Archer]

13 hours ago, JamesPa said:

A couple of the fancoil companies advertise 'light cooling' mode, basically keep the flow temp above the dew point and lightly blow air over the radiator.  It's entirely plausible that this is sufficient to make a difference in the UK climate and could be done by adding accessory fans to ordinary radiators.  

This is one of the options that we are very interested in (non-condensing cooling). Our current system is steel warm air ducts - so we could potentially send cool air around the system but only if it's above the dew point. We're considering adding a wet system and I was looking at Jaga who are one of the FCU suppliers who advertise light cooling. As a bonus they have very handsome (also very pricy...) looking rads. Who was the other company you saw out of interest? 

 

Heat Geek have a video online showing why it doesn't work very well with conventional radiators + computer fans. The rads are set up with the water entering the bottom of the panel and relying on hydronic convection to heat the whole radiator. In the experiment they did, the chilled water just sat at the bottom of the radiator, limiting the cooling output. The lower temp fan assisted/ fan coil rads use a different design which is supposed to be more effective in cooling modes. 

[JamesPa]

9 hours ago, Archer said:

Who was the other company you saw out of interest?

Myson ivector2.  Reading the spec again it's unclear whether this offers above dew point cooling or not.  I can't see a condensate drain so I think it probably does.  Also I then its stelrad that offer a variation of a normal radiator with the fins cut along the middle so they can insert computer fans in a line.

 

I have no idea of any of these work, they are all expensive.