ASHP installer says leave hot water demand on constantly

[Happy Valley]

The installers are finishing off and today will run through how it all works.

 

Yesterday they mentioned that the hot water demand should remain on constantly so that it just tops up (from say 35 to 50 degrees) occasionally rather than running it in the night once from cold. We have a 210 litre tank in a very well insulated house. 3 people who don't use much hot water. Is this how anyone else uses theirs to maximise efficiency?

[joe90]

Is this with an ASHP? I did this with mine initially but plan to time it to take advantage of E7 and/or solar panels.

[Happy Valley]

Just now, joe90 said:

Is this with an ASHP? I did this with mine initially but plan to time it to take advantage of E7 and/or solar panels.

 

Yes another Ecodan 8.5kW system here!

[ReedRichards]

Running a heat pump in the night will minimise its efficiency of operation because it is colder at night than during the day.  But if you have an Economy 7 tariff or similar it would be worthwhile.  In winter I leave my hot water heating on from 06:30 to 22:30 with the temperature set to 50 C; this is to ensure I have hot water whenever it is needed.  In summer I heat the cylinder via my solar panels on sunny days.   

[Kevm]

I run mine once in the middle of the day.  Apart from being a bit more efficient because it's warmer outside, having the DHW kicking in a lot means the heating is going on and off, which isn't good for efficiency.  Having said that, we don't use a lot of HW from the tank as we currently have electric showers.  No solar, just single rate electricity.  

[ProDave]

My ASHP is timed to start heating DHW at 11AM.  This is to stand a reasonable chance of there being a useful amount of PV generation by then and doing the bulk of the DHW heating then is one of the ways I maximise self use of the power from the PV panels.  It then remains on until 10pm to catch people who have a late shower and get enough heat back into the tank for someone that wants a morning shower. *

 

But your installer clearly does not understand how an ASHP works.

 

"so that it just tops up (from say 35 to 50 degrees) occasionally"

 

It does not work like that.  Mine has a parameter you can set which sets the hysteresis.  i.e. how much below the set temperature does the tank have to get before it starts re heating.  15 degrees would be an unusually high setting for this and could leave you with water that is not hot enough because it has not turned on yet.

 

* I also heat the DHW with a PV diverter so any excess is going to the immersion heater.  Typically the ASHP will heat the DHW to 48 degrees and on a sunny day it might end up over 60 degrees.  Often that means the ASHP does not do any DHW heating in summer.

[Radian]

31 minutes ago, ProDave said:

* I also heat the DHW with a PV diverter so any excess is going to the immersion heater.  Typically the ASHP will heat the DHW to 48 degrees and on a sunny day it might end up over 60 degrees.  Often that means the ASHP does not do any DHW heating in summer.

Remind me how much PV/orientation you have if you don't mind...

[George]

35 minutes ago, ProDave said:

 

 

* I also heat the DHW with a PV diverter so any excess is going to the immersion heater.  Typically the ASHP will heat the DHW to 48 degrees and on a sunny day it might end up over 60 degrees.  Often that means the ASHP does not do any DHW heating in summer.

 

Just on this - I looked at the Eddi device but it says it can't hook up to a heat pump controlled immersion. Or do you have a twin immersion tank?

[ProDave]

7 minutes ago, George said:

 

Just on this - I looked at the Eddi device but it says it can't hook up to a heat pump controlled immersion. Or do you have a twin immersion tank?

You probably can't link an off the shelf PV diverter to an ASHP controlled immersion, at least not without a thorough understanding of how the ASHP and the PV diverter actually work and switch the immersion.

 

In my case it is a home made PV diverter that uses a solid state relay to burst fire the immersion heater.  The ASHP controls the immersion by switching on a contactor.  Once you boil it down to that level, I just connected the contactor contact and the SSR contact in parallel.  In fact I used the ASHP's immersion control box as a convenient metal box to mount my SSR so it now contains both and just a low level switching cable to my home made PV diverter.

 

But I don't let my ASHP control the immersion heater anyway, that function is turned off.  If you have an unvented cylinder supplied by treated mains water, then the wisdom of this forum said there is no need for a legionairs cycle so just turn that function off and connect your immersion to the Eddi.

[SteamyTea]

22 hours ago, ProDave said:

If you have an unvented cylinder supplied by treated mains water, then the wisdom of this forum said there is no need for a legionairs cycle so just turn that function off

No need for it for any type of cylinder, it is a paranoid nonsense.

The problem is with unserviced, badly designed and maintained, air conditioning units, not peoples domestic hot water.

If it was, we would be reading about thousands of cases every week.  The WHO estimates 10 to 15 cases per million of population for Europe, Australia and the USA.  About half what road fatalities are in the UK, and a ninth of the USA fatalities.  And they are fatalities on the roads, Legionella does not kill everyone that gets it.

Or put it this way, have any of us met someone that has had it?