Air source/Heat Pump operation help

Mikesww

Air-source hot water system!! 

Can anyone help me tweak the settings to ensure it’s running as efficiently as possible, and answer a couple of questions? 

Its an air-source system; so a big tank under the stairs, big square box on the roof with a fan (like air-con) and we’re electric only - no gas here. 

We rent, and the system is about 3 years old. It’s made by Dimplex.

I’m really struggling to understand the most efficient settings and timers. The instruction manual is more aimed at the installers, not the user. 

There are 3 modes - Eco, Comfort and Frost Protect with a timer, so I can set one of those three modes between certain times. The manual doesn’t tell me the best way to use those modes and I can’t find this info online.

There’s a ‘target temperature’, which I have set to 65c. But that confuses me because on other posts here, people seem to say it won’t reach that target - another post said to set it low. 

There’s also an electric mode and BOOST button. Which I never use, because I assume it will heat the water only with the electric element.

It’s very ‘sensitive’ I.e. if we run out of hot water (after a very long shower or bath) it will take most of the day to heat back up and even 24 hours later, it wouldn’t be really hot. 

I have no idea what the differences are between the comfort or eco modes. I assume ‘frost protect’ is basically off, but a little boost now and again to stop it freezing.. 

Right now, it’s set as frost protect overnight, comfort mode in the early hours until 10am, eco mode during the day, then back to frost protect for the evening. 

Does anyone know - would it be more efficient to just have Eco mode on 24/7? Is that what it’s designed for? Or have I set it up correctly with comfort for a couple of hours in the morning, then Frost Protect overnight? 

In my current settings, Eco mode stops and it switches to frost protect at 6pm, until comfort mode kicks in at 5am the following morning. So would it be using loads of electric to heat the whole tank again at 5am? 

We’ve never had air-source hot water, and just want to ensure we’re using it in the right way! In addition, I have no idea how they’re supposed to be used effectively. I just guessed at the correct settings. It’s hard to play around with it - I tried once and then had no hot water for 48 hours!! 

Any advice or help would be appreciated - there’s hardly any info online either about how to use them efficiently, the difference between modes, or if they should be left on 24/7. 

Thankyou

Rodders53

What model of Dimplex ASHP HW tank?  Is it this beast? https://www.dimplex.co.uk/product/edel-hot-water-heat-pump

matelodave

A bit more info please - what model Dimplex,, we could then have a shufti at the documentation.

Have you got rads or underfloor or fan coil units. What other controls are there (other timers or room stats, do the rads have trv's). What size hot water tank have you got, does it have an immersion heater. What electricity tariff are you on.

Generally any heatpump wont heat above 50-55 degrees so if you've got yours set to 65 then it will use the boost.backup heater which will increase your energy costs considerably (the biggest mistake that most people make) however if you've got the boost heater disabled then the heatpump could well try to heat the hotwater tank all day and all night and never achieve 65 degrees.

Rodders53

OK I've read the Dimplex Edel manual and spec sheets.  It's a HW cylinder with the HP on top going to air vent pipes to the outside.
COMFORT will use the 1.2kW immersion heater as well as the Heat Pump.
ECO uses the heat pump only.  
FROST/FREEZE  is just that to kick HP and/or immersion in to prevent the cylinder freezing.
BOOST will use both HP and Immersion.

There's an Electric only mode for Immersion heater only use when the HP has a problem.  

I don't see anywhere that the immersion can be permanently switched off via the installer manual?  Electric mode off in the menus doesn't do that (as I read it).

Dimplex claim the HP will reach 60C but that 65C is only possible with the immersion as well. It's more likely that 55C will be achievable with reasonable HP efficiency.
How long are the air ducts to an external wall? 

Do you have economy 7 or a single rate meter?

With very cold outside air at the moment the HP efficiency may well be poor, so taking a longer time to raise the water temperature.  Note Dimplex suggest it needs to be on for a minimum of 12 hours a day (page 21 of installer manual). They claim a max1300W heating from a m\x of 700W input.  The two tank sizes are 200 and 270 litres.  Reheat times from 10C incoming water (it'll be lower this time of year) may be based on either HP alone or HP and immersion use; but are over 7 and nearly 10 hours.  

I'd suggest trying it on ECO mode at 55 to 60C max, and play with the time it's nominally on for to get HW when you need it after a full 24 hours+ on? Or if you are heavy HW water users, then consider adding some COMFort times in using the imersion?

Mikesww

Thanks so much for all the info so far. From what I can see, there’s hardly any info on how to use them effectively online! All I can find is technical info.

Yeah, that’s the one Rodders. Edel 630 - Dimplex. 

I don’t know what fan coil is but we have electric rads in the house. They’re Rointe and controlled via an app on my phone or by using the screen on the rads. I know they use a lot of electric but we’ve been told as far as elec heating goes, they are the better of a bad bunch. Our heating isn’t night storage. 

So the air source bit only does our hot water - not underfloor heating or radiators.

Matelodave, I think it does have an immersion because when you press ‘elec mode’ the fan instantly stops and the screen flashes ELEC. We’re on a normal tariff, and just switched to Neon Reef from Bulb. Not economy 7.  You saying about it being set to 65, that’s exactly what I’m thinking... are we just wasting energy trying to get it to 65, which it will never do!?

Rodders - Thankyou for all the info so far. That’s really kind taking the time to do that. The tank is downstairs, the pipes came out of the top, then disappear behind the tank where I guess they go into the wall/a duct and upto the roof (one storey) . 

It’s a 200L tank. I’m on furlough and other half is working from home so we are using more water than usual, and recently the hot water is running out slightly after the second shower. But that could also be because of the cold weather. 

Honestly, thanks so much for all this info. 

So Comfort mode will use electric too? I didn’t know that... I thought comfort meant the fan would work harder (lol) to provide hotter water!!

Mikesww

I just want to get that sweet spot where we’re not wasting energy, but have hot water when we need it!! 

I just grit my teeth and expect bills to be higher each winter because we’re all electric. We’ll go through 800-900 units each month in the winter and then in the summer we drop down to 150-200 units a month. That’s based on actual readings. We only heat the rooms we’re using, the majority of appliances are A+, we try to keep the rads down at 19/20c. Plus it’s a new build (3 years old) and has good insulation. But every external wall is mostly exposed. 

Do you reckon I should be using frost protect during the night? Or am I just letting the water cool, to then re-heat it again by doing that? 

So you guys reckon Eco mode 24/7, a few hours of comfort in the morning, and turning the target to between 50&60? 

Again, really appreciate your help and tips!!!  Thanks 

matelodave

Our hot water is generated by a heat pump and we only run it at 45 degrees. It's a 200litre tank and we can get two showers plus all the hot water we need by running it for less than two hours a day (hot water is activated between 0430 and 0630 so there's hot water for morning ablutions). We've still got enough hot water for two more showers in the evening if we want to

We have a dishwasher so there's not much washing up but we are conscious of our hot water consumption. Don't let hot water run down the sink, don's rinse stuff in hot water and avoid drawing of tiny amounts just to wash hands especially if there are long pipe runs between the tank and the tap. If you have to draw off half a gallon or so before the tap runs hot then you are leaving half a gallon of hot sitting in the pipes to get cold. Our shower has an eco shower head which reduces the flow to around 6lpm and we don't stand in there for ages, about 2 minutes for me and 3-4mins for her.

I'd try turning your temp down to 50-55 degrees and running in Eco mode overnight so you've got a tankful of hot water when you get up as it appear that the heat recovery times are quite protracted - take more notice of your leccy consumption to see what effect it has. Don't forget using comfort or boost or increasing the temp above 55 will activate the immersion which will cost you more than running the heatpump in Eco mode for a longer period of time.

You get between 2-3kwh of heat from 1kw of leccy with the heat pump but only 1kwh of heat using the immersion.
It takes around 12.8kwh to heat 200 litres of water from 10-65 degrees but only 10..5kwh to heat it to 55 degrees - the spec suggest that it takes around 7 hours to heat a 200 litre tank to 55 degrees so you need to have it on for a long time to get the tank up to temperature.
There's no point in being on an e7 tariff, most of your heating is during the peak periods and the hot water tank probably uses lest than 3-4kwh a day when used in ECO mode (even if you run it 24/7) so you need the cheapest single rate leccy you can get.

TBH your consumption doesn't sound to be outrageous - our heatpump does the heating as well and in January got through 1400kwh but we do have a largish detached bungalow out in the fens with adequate rather than good insulation and it's heated all day and sometimes all night if its ever so cold outside.. Our annual consumption is around 7200kwh which I'm quite happy with. We are also with Neon Reef

Mikesww

Matelodave. that’s really useful stuff, cheers. I had no idea the comfort mode used the immersion - I thought only ELEC mode would do that. I’m guessing BOOST uses immersion too? 

The house is upside down (bedrooms downstairs) and not big by any stretch. But because of the layout, the water has a long way to travel from the tank (downstairs) to the kitchen (upstairs) and the bathroom (far corner of ground floor). I know we waste a fair bit just bringing hot water to the taps. 

Good to know about your electric too. Makes me feel better... we used to be with Green.Energy, but prices have just gone up, so found a good 12month fixed deal with Neon Reef. 

From what you’ve said, I reckon by going into frost protect at about 1800, then comfort at 5am, we’re heating the tank with the immersion, which is defeating the object. 

I’ll turn the target down to 50c, put it on ECO 24/7 and tweak from there... and hope I don’t get it in the neck tomorrow morning hahahaha. 

Thanks guys. You’ve really helped me out. I now understand how it’s supposed to work.

matelodave

My heat pump is a lot more powerful than yours (11kw) that why it can heat the water faster - I think yours is only rated at around 1.4kw* plus another 1.2kw with the immersion so even with both of them on it's going to take longer than a normal tank with a 3kw heater to get hot (200 litres from 10 to 55 degrees takes around 10.5kwh, with 3kw will take around 3.5hours and another 45mins to get to 65).

The sums are pretty easy or you can use this calculator to work it out - https://bloglocation.com/art/water-heating-calculator-for-time-energy-power.

*the rated output is what the heatpump delivers rather than what it's electricity consumption is, so you would probably only be consuming between 500w and 750 watts of electricity to get 1.4kw of heat. So to produce 10.5kwh with the heat pump will use around 3.5-5.5kwh. Using the 1.2kwh immersion heater as well will nearly halve the time but probably push the consumption up to around 8 kwh and cranking it up to 65 could increase it to around 10kwh. You do the sums and see how much it costs

Mikesww

Nice one. I’ll have a look at that calculator. 

I’ve actually just checked the timer out and I had it set for 8hrs in comfort mode, and 4 in ECO. FP all night. 

I’ve now changed it to 15hrs in ECO overnight, and only 2 hours comfort in the morning, then FP during the day. Hopefully that will give enough hot water and if not, I’ll up the ECO mode.  Plus I’ve put the target down to 50c. We’ll see how that goes but I might need to up the ECO times. 

Am I right in saying that the general idea to get the best out of air source is ‘low and slow’ instead of small peaks of comfort during the day? 

matelodave

Yes - think of it like driving a car - you get far better MPG when driving gently at say 50  rather than thrashing the pistons out at 80 to get there a bit quicker.. It may take a bit longer to get there and its'll be a bit boring but you'll save a lot of fuel doing it.
I've had my ASHP for over ten years and it's much more economical to run at low temperatures than it is if I crank them up to heat the place a bit quicker so to compensate I don't turn it off, just down a couple of degrees overnight. This time of the year when it's freezing outside it virtually runs 24/7 but we don't have a cold house.