Hi Weoleyric,

Welcome to the forum.

To try to answer your question, it very much depends how your original system is designed to operate and what duties your gas boiler actually performs. Since you mention installing a hot water cylinder, then I assume that your gas boiler is providing all your hot water, but does it also provide any form of heating? The fact that your ASHP is only rated at 4kW, would probably mean that it would struggle to provide all your heating and hot water demand in the depths of Winter. What is the size of your home and the heat loss calculations?

@Derek-M Thanks for the welcome and your response!

To clarify, our ASHP Hybrid system is setup to use Gas for hot water, and electricity (priority) with gas backup (when the ASHP can't provide the required level of heat) for heating.

Our home is a small 3-bedroom semi-detached in Newcastle-upon-Tyne. It is well insulated, with double glazing, cavity wall insulation and loft insulation.

I've checked the Daikin Altherma Hybrid Monobloc Heat Pump installation manual, and it does refer to the option of having a hot water tank, however, I can't clarify if a hot water tank could be used *without* a hybrid gas boiler attached, too (to allow us to go all-electric).

The worst-case scenario for us is that the Daikin Heat Pump *isn't* capable of working without a hybrid gas boiler, and are looking at a brand new ASHP to go all electric. Fingers crossed that isn't the case!

Hi @weoleyric

It is difficult to give definitive advice without knowing exactly how your system is connected and configured, but based upon the information supplied I think that you may be able to consider the following.

I see no reason why it should not be possible to completely remove the gas boiler and install a hot water cylinder. I would suggest a cylinder, with a large area heating coil suitable for use with a heat pump, and also two immersion heaters, one for use with an electrical power diverter unit to use power from your solar PV system, and one fed directly by mains power for when there is insufficient solar energy.

Since you state that you have a small, well insulated, home, your present heat pump will probably be sufficient to keep your home at the desired temperature, and may even be able to provide much of your hot water even during the Winter months. Do you have any heat loss calculations for your home? Rather than installing a larger heat pump for the few days I suspect your present system may not meet demand, you could consider buying an electric fan heater or similar.

The fact that you have a solar PV and battery storage system is highly useful, and should allow you to maximise the operation of your system, and minimise the running costs.

Here are some suggestions for consideration. 

When heating is required by the heat pump, the primary energy source should be solar PV when it is available, then your battery storage when there is insufficient solar PV. Drawing power from the grid should be the last resort, though of course you could fill your batteries and run your heat pump overnight on one of the low rate tariffs.

To provide hot water the primary energy source should be excess solar PV via a power diverter unit (iBoost, Solic, Immersun etc), then hot water heated by the heat pump when excess solar is insufficient, and direct grid supply as a last resort.

We have a somewhat similar set up to you, in that we have a gas boiler that can provide both heating and hot water, but via a hot water cylinder. We also have a 4kW solar PV system, but without the battery storage, and this provides the majority of our hot water from Spring through to Autumn, via an Immersun power diverter unit. For the past two weeks our gas boiler has been shutdown completely, our hot water has been produced solely by solar power, as has much of our heating via an Air to Air ASHP. Most days recently there has been sufficient solar energy to both provide hot water and heat our home, often with excess left over. We boost the indoor air temperature to 22C to 23C during the daylight hours, so that the heat pump has less work to do during the colder nighttime period.

If you have any further question or require clarification then please get in touch.

@Derek-M Thanks for the detailed advice. I really appreciate it!

I wasn't aware of the iBoost/Solic/Imersun, etc so I'll check them out.

I'll keep you posted on what we find!

@weoleyric sorry to butt in here - if I was starting again with a new cylinder I'd consider Solar Thermal water heating which I believe means two coils. Depends on the available roof space for more panels of course.

Posted by: @heat-pump-newbie

@weoleyric sorry to butt in here - if I was starting again with a new cylinder I'd consider Solar Thermal water heating which I believe means two coils. Depends on the available roof space for more panels of course.

Thank you for your input Newbie, how are your smoke signals progressing, have you had any replies?

I didn't suggest solar thermal because a 4kW solar PV system should be able to provide both hot water and heating for most of the year, though installing a hot water cylinder with two heating coils and two immersion heaters would cover all bases for further expansion of the system should it be deemed necessary.