Air Source Heat Pumps

richardc1983

The immersions I assume are there as backup, but I reckon they can be overidden so they come on any way with the heat pump. Perhaps this is the reason.

The heat pump alone is no way causing the consumption mentioned!

samtheman1k

richardc1983 wrote: »

The immersions I assume are there as backup, but I reckon they can be overidden so they come on any way with the heat pump. Perhaps this is the reason.

The heat pump alone is no way causing the consumption mentioned!

The immersions have to come on as the regs say hot water must be heated to 60degC to kill all the little bugs that reside.

However, eugeneg, you haven't actually said whether your HP heats up your hot water or not? Are you immersion heaters purely electric?

richardc1983

Judgin by the specs it says its a Electric boiler so im thinking its purely for hot water and doesnt integrate with the heat pump.

Cardew

samtheman1k wrote: »

The immersions have to come on as the regs say hot water must be heated to 60degC to kill all the little bugs that reside.

However, eugeneg, you haven't actually said whether your HP heats up your hot water or not? Are you immersion heaters purely electric?

If you look at the links he gave the 13.5kW immersion heater is to heat the water in the thermal store for the radiators.

He talks of a 4kW and 2kW immersion heater which had I assumed is the boost for the Hot water to bring it up to the 60C for safety reasons. i.e. the domestic hot water would be warmed to the temperature in the thermal store by a coil running through the tank.

However I take your point that this assumption may not be correct and the ASHP may not be heating the domestic hot water at all.

richardc1983

Cardew if you look at the specs on the site it quotes 13kw for the electric immersion.

Output immersion heater13.5 kW

Cardew

richardc1983 wrote: »

Cardew if you look at the specs on the site it quotes 13kw for the electric immersion.

Output immersion heater13.5 kW

Richard,

If you look at my post above(164) I raised the issue of 13.5kW immersion heater. I wrote:

According to the link you gave you have a 13.5 kWh Immersion heater in the 125litre heat store? So where are the 4kW and 2 kW immersion heater.

That huge powered immersion heater is for the thermal store - that is quite clear cut - and the thermal store is to provide hot water to the radiators.

The issue here is the 4kW and 2 kW that eugeneg talks about(see his post). The suspicion is that they are nothing to do with the ASHP CH system but a conventional domestic HW system - albeit I have never seen a 4kW immersion heater.

Hermann

Looking at the links I read it as the system could have a total of 13 kw over two immersions. The reason that you're seeing immersion values you don't recognise is that the system controls a larger immersion (6kw) down to the values eg 2kw, 4kw according to the settings (knob 102).

This system looks to have an enormous range of controls and operating modes, including some that don't use the heat pump at all.

I think eugeneg really needs to get to grips with understanding the various operating modes and options to get the best from the system. The installer may not have fully understood them himself or may have just left factory defaults set.

Some examples include the summer, spring/autumn , auto settings. I think I might be inclined to use the spring/autumn mode with the 3hr extra hot water when needed, and then time my hot water use to that three hour priod.

Other things worth getting to grips with include the tariff setting on p24 of manual, this could have a big effect if its set for tariffs you don't have!

Centralised load control/Tariff
In those cases centralised load control or tariff control is
used this can be connected to the terminal block (14) on
the load monitor card (2), which is positioned behind the
centre front cover.
Tariff A: To limit the electrical output to half of what is set
with max electrical output knob (101), connect a potential
free contact between 5 and 7 on the terminal block (14).
Tariff B: When the complete electrical output is to be disconnected,
a potential free contact is connected between
6 and 7 on terminal block (14).
Tariff C: When the complete electrical output together
with the heat pump is to be disconnected, a potential free
contact is connected between 12 and 13 on terminal block
(14).
A closed contact results in the electrical output being disconnected

Also p37 refers to hot water settings.

Menu 1.1 Start temperature HW
The temperature when the heat pump starts to work with
the hot water heater is set here.
The value can be set between 25 and 50 °C. The factory
setting is 45 °C.
Menu 1.2 Stop temperature HW
The temperature when the heat pump/immersion heater
should stop heating the water is set here.
The value can be set between 30 and the set value in
meny 1.3. The factory setting is 50 °C.
Menu 1.3 Stop temp. XHW
The desired stop temperature for extra hot water is set
here.
The value can be set between 40 and 80 °C. The factory
setting is 65 °C.
Menu 1.4 Interval XHW
How often the hot water temperature is increased from
the normal level to the “Extra hot water” level is shown
here.
The value is adjustable between 0 and 90 days. Periodic
Extra hot water is shut-off at value 0. Extra hot water is
started when the value is confirmed. The factory setting is
14 days.
Menu 1.5 Next XHW action
Future increases to the “Extra hot water” level are shown
here.
Menu 1.6 HW run time
How long hot water heating has been in progress is shown
here (accumulated).

Then there's the adjustable heat curve.
There's lots more as well so it really needs setting up correctly for your installation and tariffs.

The only point I can see for using it as a heat store using immersions might be using off peak Economy 7 tariff to heat up store overnight on cheap electric. If you're trying to do this first you need to be on the tariff, you don't mention it, secondly the system needs setting correctly to do this efficiently. The sums need to be done carefully to work out whether this is economical.

One final point is storing all that hot water, and keeping it hot takes a lot more energy if the store and pipework isn't well insulated. The store will have some insulation but it won't be a lot. If the store is in a draughty, cold old garage you're going to lose a lot of heat. its better of in a small insulated enclosed space to keep the losses down.

With no heating or hot water drawn overnight you should be looking for a 1c or 2c drop in store temp. If its dropping by more (without drawing anything from it) then look into why. If its dropping by 10c + you're haemorrhaging heat and that will cost you especially if you're using immersions to keep it up to temp 24hrs a day.

In short understand and use the settings, and insulate the pipes and store!

Hermann

One other thing is the central heating settings.
When Using a Heat Pump the oversized radiators are used to account for the lower temps of the flow.

Make sure your settings are outputting these low temps to the CH system otherwise the immersions will kick in to boost the flow temps up. You don't want this, you want to just be using the heat pump for the CH flows.

Hermann

richardc1983 wrote: »

Cardew if you look at the specs on the site it quotes 13kw for the electric immersion.

Output immersion heater13.5 kW

The install manual seems to reference a max of 13.5kw. It mentions a factory standard fitment of a 6kw element which is limited to either 4kw or 2kw depending on mode with additional kw applied in boost situations.

Cardew

Thanks Hermann, good advice. I hadn't read the full instructions.

What is worrying is the brochure states for small properties and is clearly designed to supplement a 'normal' CH system.

Given it is now supplementing an electrical CH ststem, as you say it is important to maximise the ASHP output.

Apart from Economy 7 this new EDF 20:20 tariff might be worth considering.