Air source heat pump vs modern electric storage heater (Scotland)

ASavvyBuyer

EVandPV said:

I'm guessing we'd maybe need to consider a bit more battery storage, a couple more Pylons ??
How do you guys heat your water when there's little to no PV ?

We heat it during the night on the Go Faster tariff. We have a time switch that switches between the Solic Diverter output and the mains at the right time. So from 02:30 - 6:30 the immersion heater is supplied direct from mains, but for the rest of the time it gets power from the Solic Diverter. In summer, the time switch is set so we just get power from the Solic, unless we get a few bad days in a row.

JKenH

ASavvyBuyer said:

EVandPV said:

I'm guessing we'd maybe need to consider a bit more battery storage, a couple more Pylons ??
How do you guys heat your water when there's little to no PV ?

We heat it during the night on the Go Faster tariff. We have a time switch that switches between the Solic Diverter output and the mains at the right time. So from 02:30 - 6:30 the immersion heater is supplied direct from mains, but for the rest of the time it gets power from the Solic Diverter. In summer, the time switch is set so we just get power from the Solic, unless we get a few bad days in a row.

Similar here, with the IBoost having a built in timer with separate summer and winter settings although tbh we rarely need trouble the mains for hot water 6 months of the year, the PV being sufficient.

Coastalwatch

EVandPV said:

Regarding the air to air units, do you have an idea of how much power they consume over the course of a year ?

We have two 2 kW units, one in the lounge the other in the lobby heating the bathroom and two bedrooms, naturally to a lower temperature. They have been in for two years this month. In the first winter we only used them during the day when solar was available and GCH outside of this. Last winter we used the ashp's only. In the two years the lounge unit has consumed approx 1500 kWh's while the other circa 1200 kWh's.

I could give precise figures but that would mean getting up in the loft to check, but it's a bit nippy up there at present, so hopefully for now these figures may suffice?

Something to bear in mind is that the last two winters down here have been on the mild side.

Coastalwatch

Further to the above, actual figures for consumption read - Lounge 1555 and Lobby 1169 kWh's. Combined monthly figures for this last winter in kWh's being, Nov 481, Dec 552, Jan 671, Feb 483 & Mar 440.

A minor proportion of these figures would have been covered by solar output. Unfortunately I've no way of knowing what this might have been!

Sitting here in the lounge on this overcast day and with just one ashp running the IHD unit indicates that we are still exporting.

Reed_Richards

Storage heaters are for people with access to a night-rate cheap electricity tariff.  You need a suitable electricity meter.  If you have cheap electricity at night you can also use that for an immersion heater to heat a tank of hot water to last you through the day.
ASHPs (air to water) are least efficient in heating your hot water tank so are a poor fit to your requirements if you don't want extra room heat.    

Polfers

Hi, Forumite

Firstly, hot water: The intrinsic problem with hot water as supplied by emersion heaters is that you may well be heating up water that, in your case, you don't need in that quantity, which will then cool and you'll need to heat up again in its entirety when you next need hot water; hardly a model of efficiency, no matter how well insulated your tank may be.

If using an instant hot water solution in the form of an electric heater (as per the item at screwfix mentioned by Solarchaser), whilst a potential solution, means the flow will be very poor indeed. This is because a domestic electricity supply cannot provide the "clout" in terms of the watts needed to achieve anything better (ask me how I know): continuing to use your kettle would fill the washing up bowl faster! Electric showers suffer from a similar fate for the same reasons, especially so when the incoming cold water supply temperature is low in the winter months. This is of course why people who use electricity for heating water generally tend to opt for some form of immersion heater/tank system.

However, there is another solution available which I have found to be extremely good at providing as much hot water as I need, when I need it, at a great rate of flow, and inexpensively, too, as it is extremely efficient:

There is a Japanese company called Rinnia (they have a presence in the UK – and no, I have no connection to them what-so-ever - https://www.rinnai-uk.co.uk/), who (amongst other things like heat pumps and solar water heaters – the latter being another potential solution, but which still needs to fill up a tank), make instant hot water ONLY solutions in the form of a natural gas or LPG gas powered system - please stop boo-ing and hissing for a moment and read on… :0)

This DOES NOT power central heating - it just provides instant hot water on demand from a small, wall mounted low / ultra-low NOx boiler that can be installed inside or outside your home. We (there are two of us, retired) do not have mains gas, so we had to opt for propane cylinders. Two of these (45kG size), supply ALL our hot water needs for a year at a cost of £85.00 per cylinder (so £170 a year – using natural gas, if you have it, would be significantly less – perhaps £100 to £120 per year to run). It provides 55 KW of power, which heats water fast and in whatever quantity we need, when we need it, it produces ver, very little in terms of greenhouse gas emissions and gives us an amazingly powerful, instant hot water supply 24-7.

Central Heating: Unfortunately, all radiator-based heating dries out the air, so you pays your money and you makes your choice. The only solution that can help here is to keep temperatures lower to minimise this effect – max 21 degrees in the lounge and no more than 18 in a bedroom - less if you’re comfortable.

We looked at installing an air to water heat pump system, as we didn’t like the idea of high-wall mounted air to air heat-pump heaters, as we have low ceilings and the ambient noise, though not too high, we found would be irritating for us, however, that’s a personal choice: if you’re happy with air blower based heating, the air to air heat pump is a more efficient and lower cost way of employing a heat pump based solution for heating only.

Air to water-based heat pumps are efficient, if less so than air to air, but of course run 24 hours a day. If you draw hot water from the (enormous) tank, your heating will cool down until the water in the tank is heated up again (a secondary store is often used to counter this effect). For obvious reasons, they are far more efficient in warm weather, than in cold weather, but you need heat in cold weather, not warm weather. Therefore unless you have a well-insulated home, which, in retrofit applications, if built (generally speaking), before the 1990’s, is far more difficult to achieve than in a new-build, as well as being potentially costly on top of a £13K plus cost for the heat pump & radiators themselves.

In our case (it may not be for you or others), we opted to insulate as best we could (house built 1985) and install storage heating (only in daytime use areas, using panel wall heaters in bedrooms and bathrooms).

Yes, these are less efficient per-se than an air source heat pump. However, using economy 7 electricity, they are “on” for 7 hours to charge up overnight at 15.14 pence per KWH. This is combined with solar panels which charge batteries to provide free electricity during daylight hours. If the batteries aren’t fully charged by the solar panels, or we use the solar energy during the day (meaning the batteries are not charged/fully charged), we can use cheap rate economy 7 electricity to charge them overnight, meaning that effectively, we use free or cheap rate electricity in the daytime.

As has been mentioned, a Heat pump has moving parts that wear out, too, and basic servicing is around £250 a year. Eventually, it will need to be replaced which won't be cheap, even though prices are gradually coming down.

We live in a 3 bed terraced house in Scotland, so it can get cold here in the winter (-10 to -15 at times). We have a front and back garden, and the back garden (where a heat pump would have to be installed in our case), meant we’d have a blast off freezing cold air from the heat pump to look forward to if sitting outside in the summer, which is something we enjoy (the garden, that is, not the blast of freezing cold air!) Our neighbour installed a heat pump 8 years ago. They never use their back garden anymore. Of course, this is just our circumstance and our choice, but it may be a solution for others. There's no one-size fits all.   

Reed_Richards

@Polfers, I can see that you are new to answering questions on the forum.  If I may give you some advice, answering a question in a thread that has been inactive since November 2020 is likely to be a waste of your time.  No matter how well and comprehensively you answered, what you wrote is unlikely to be still relevant to the OP over 3 years later.  

pete-20-11

Reed_Richards said:

@Polfers, I can see that you are new to answering questions on the forum.  If I may give you some advice, answering a question in a thread that has been inactive since November 2020 is likely to be a waste of your time.  No matter how well and comprehensively you answered, what you wrote is unlikely to be still relevant to the OP over 3 years later.  

It might be useful to someone else. Not everyone asks their questions, just gets the answers they need from what others have posted. 

Reed_Richards

pete-20-11 said:

Reed_Richards said:

@Polfers, I can see that you are new to answering questions on the forum.  If I may give you some advice, answering a question in a thread that has been inactive since November 2020 is likely to be a waste of your time.  No matter how well and comprehensively you answered, what you wrote is unlikely to be still relevant to the OP over 3 years later.  

It might be useful to someone else. Not everyone asks their questions, just gets the answers they need from what others have posted. 

You're right.  But any thread that is not followed-up by others rapidly disappears from sight.  So to be useful to others a week or more from now, those others would have to guess the right search terms to find this thread again. 

QrizB

pete-20-11 said:

Reed_Richards said:

@Polfers, I can see that you are new to answering questions on the forum.  If I may give you some advice, answering a question in a thread that has been inactive since November 2020 is likely to be a waste of your time.  No matter how well and comprehensively you answered, what you wrote is unlikely to be still relevant to the OP over 3 years later.  

It might be useful to someone else. Not everyone asks their questions, just gets the answers they need from what others have posted. 

It might not be very useful, though; there are a few assumptions and folk-wisdoms in there that aren't borne out in practice.