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How can I get my Daikin Altherma 3R to be more efficient with Economy 7?

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(@bob77)
Trusted Member Member
292 kWhs
Joined: 1 year ago
Posts: 36
Topic starter  

Hello,

I’ve been lurking on the forum for a while and thought it was time to join. I have recently had a Daikin Altherma 3 R (low temperature split) system installed as part of a major renovation project. 

My house is a 1960s three-bedroom end of terrace and we have just added a single-storey extension that doubled the size of the ground floor. Previous heating was Economy 7 storage heaters plus electric underfloor in the kitchen and bathroom, and the bills were horrendous even before the latest increases - we were using around 12,000 kWh per year (a few years ago it was over 14,000).

There is gas to the street but for some reason it was never connected to the house, and it seemed stupid to put a new gas CH system in in 2022. So we took the opportunity to put underfloor heating through the entire ground floor including the existing house. Upstairs are radiators in the three bedrooms (bathroom is small and we kept the electric UFH to avoid disruption).

We have had quite a few teething problems, which were eventually pinned down to faulty flow sensors in the indoor unit. Now they have been replaced we have finally got error-free operation, and I’m keen to work out the best way to run it with our Economy 7 tariff (or whether it even makes sense to continue with E7).


   
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(@oswiu)
Reputable Member Member
793 kWhs
Joined: 2 years ago
Posts: 121
 

Firstly on hot water, obviously just schedule it to come on overnight, perhaps in addition to whatever your current schedule is. 

Next on using your house to store heat during cheaper hours, there are a few things that come to my mind, the most basic of which being a simple schedule. 

How is your system currently controlled? Do you have a room thermostat or is it purely on weather compensation? 

If it's the former then you could increase the target temp during economy 7 hours with whatever controller that uses, if it's the latter you could do the same with Daikin's own controller but with the water temperature of the circuit "leaving water temperature". You might need to lower the default temperature first. 

I haven't been on an economy 7 tariff for years, so I can't remember how different the rates are, but you should be aware that a heatpump will use a disproportionate amount of extra energy to heat water to a higher temperature, so if you do go with a house buffering, then you should monitor it closely to check it's working efficiently. Also if your house doesn't hold the heat well, then it might be pointless, but I should imagine that it's more likely to work with under floor heating than rads.

I suspect none of this heat buffering stuff would work when it's actually cold except for your hot water, so I would consider if you need the tariff anymore, eg do you have an electric car? 


   
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(@kev-m)
Famed Member Moderator
5561 kWhs
Joined: 3 years ago
Posts: 1299
 

Hi and welcome to the forum.  I had E7 heaters pre ASHP using close to 20000 kWh per year.  Now down to 6-7000.  I went onto a single tariff; it wasn't worth continuing with E7 as I have all radiators.  If you have ufh and a solid concrete floor it could be worth (over)heating it up overnight on E7.  You'd have to try it out for energy consumption and comfort.  My guess is you might save a bit but would lose the nice constant room temps an ASHP gives.  I hated the hot in the morning/cold at night feeling the storage heaters gave. 

 


   
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(@bob77)
Trusted Member Member
292 kWhs
Joined: 1 year ago
Posts: 36
Topic starter  

Hello, I posted this in the welcome thread so I wasn’t expecting to get my own thread 😀 

Some more info:

Electricity rates: night 23.9p, day 36.8p so quite a significant difference. 

Currently the installer has left it on a constant flow temperature of 48C, as he said to “warm up the house” as we had lots of damp from screed and plastering etc and the house was open to the elements for longer than we had hoped. 

He also set up a weather compensation curve and said I could switch over to that if I thought the heat was excessive (which I think it probably is!)

The curve he set up appears to simply have 50C below 5C outdoor temperature and then a slope down to 30C at 25C, which seems quite high to me all round!

Downstairs we have two zones, one in the main open plan kitchen/dining/lounge and one in the TV/family room (which is not really in use yet as it’s not decorated). These are controlled by Hetta thermostats which control the UFH manifold. Upstairs are radiators controlled by a single Honeywell wireless thermostat, with TRVs on the rads. 

Both downstairs and upstairs thermostats are connected to a single input on the heat pump, in other words it is operated as a single zone rather than having different flow temps for the UFH and the rads. That seemed a bit strange to me given the heat pump has the capability of running two zones with different flow temperatures - presumably if it was set up like that then it could have a lower temp if only the UFH was calling for heat?

 

DHW is set up to heat between 1am and 5am, to 52C plus a second schedule to reheat to 45C if needed at 5pm. I changed this from the “schedule plus reheat” mode as otherwise if we had a bath/shower in the evening and dropped the tank temperature it would reheat before the E7 kicked in. 

The UFH is in screed. The old part of the house has fairly thin screed over the old concrete slab whereas the new part is thicker screed over foam insulation. 

Should I be trying to heat up the floor overnight and then just let it act as a radiator during the day, like the old night storage heaters which were stone cold by mid afternoon?


   
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(@bob77)
Trusted Member Member
292 kWhs
Joined: 1 year ago
Posts: 36
Topic starter  

I would also add that having checked out the Bulb tariff for non Economy 7, the rate is only slightly lower than my existing tariff (34.2258p versus 36.7678p for E7 daytime rate, and 23.9463p night-time)

So in order to beat the non-E7 rate I would only need to have 20% of my usage overnight. I try to put the dishwasher, washing machine etc on overnight using timers as far as possible. 

Cheap rate runs from 11.30pm to 6.30am in winter and I usually get up at 7am so it seems the best bet would be to have the DHW heat up in the early hours then have the underfloor heating and radiators warming the house up from say 4am until 6.30am. 

I work from home so don’t want it to get too cold during the day but we have improved our insulation with the new extension so the house seems to hold the heat quite well. We also have a wood burner which we like to use for ambience but also throws out a lot of heat. So in fact we might be ok with just heating overnight and topping up with the wood burner when needed, unless it gets really cold.  

It’s been so mild this autumn that it’s hard to tell at this stage. I don’t think we have even had an air frost yet, although the weather does look like turning colder next week. 


   
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 Mevl
(@mevl)
Active Member Member
44 kWhs
Joined: 5 months ago
Posts: 3
 

@bob77 Thank you for sharing all the information about your Home.

We also own a 3 floor terrace home build in 1892 in the Netherlands. When we bought it was inefficient ruin. 3 years it took us to convert the house into our home. 

We predicted issues with Gas, so we purchased Daikin Altherma 3 and waited 6 months for the newest outdoor unit that came to market. 

This year it was poor summer and I'm here to learn about optimising settings on heat pump. 

 

It is December 13 and we are quite lucky as the temperatures are above 10ºC so far I keep the floor heating completely off.

You mentioned schedules. Do you know how long it takes your heatpump to warm up entire water tank? I'm planning to use evening tarif to heat up the house.

Have you figured how much time is needed to heat up a room (kitchen, Livingroom for example) you mentioned 4am to 6.30 am is that sufficient?

Did you do any new schedules for 2023?

 

thank you in advance.

 

Miro 

 


   
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