Daikin EDLA08EV3 pre install

Hardware
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After months and months of research and quotes from Octopus, Heat Geek and British Gas I have finally got to the point of committing to the install.

I have chosen British Gas as they have proposed a better install over Octopus (and also price matched them). Both recommended a Daikin EDLA08EV3

The survey was light years ahead of Octopus, using far more sophisticated and thorough heat loss calculations, were far more flexible on installation options and have designed the system to 42.5c at -1.7c. They even followed up with pages and pages of detailed information which has been very useful.

BG were also Ā£7000 cheaper than the local Heat Geek installers, (the BG total price to pay is just over Ā£3000 including a 210l slimline HP cylinder and 25l volumiser) for a similar install.

Iā€™d like to run by the forum the radiator proposal, just to make sure it is sensible. (I have followed Matt Dā€™s posts and journey and am particularly keen to ensure the radiators are about right!).

4 bed mid 50ā€™s semi including extension in 2007 (which doubled the house from a 2-4 bed)

135m2

Insulated cavity walls on 50ā€™s house

200mm loft insulation

Electric underfloor heating in kitchen extension

10 radiators (plus 1 proposed addition for landing)

BG heat loss calculation 6.2kW (Octopus 6.9kW)

BG have designed the house @ 21c everywhere, including bedrooms (other than 22 for bathrooms), to maintain that temp throughout.

The bedrooms at 21c is the main question.

Is this in the real world likely to be ok? We donā€™t want overheating bedrooms, but also recognise that having bigger radiators, may actually be a benefit to the system as a whole.

BG will install TRVs to the bedroom radiators only.

This is the radiator schedule, which Iā€™ve calculated should have enough capacity at 30c flow temp to allow the 8kw Daikin to modulate low enough.

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Everyone is different about how they like their bedrooms, but for me (and online searches suggest similar), 18c is about right for sleeping. 21c would be way too warm unless youā€™re sleeping under a single sheet but for duvet sleep, Iā€™d be sweltering at 21c and reaching for a fan.

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Welcome @Ginger

I think youā€™ll be fine with the 8kW Daikin and the radiators you are proposing.

I have got the 6kW Daikin and have in total 6.8m length of 600mm high K2 (total volume about 40L). Thatā€™s about half what you are proposing. I have also got a 20L volumiser. I get some cycling in warmer weather but I think you will have enough to avoid that in most situations.

Assuming the heat losses are accurate (or at least consistent) then the proposed radiators look well sized for the rooms.

For the bedrooms 21C would be too warm for most people. The TRVs will allow you to control to a lower temp. That means that you canā€™t really count those radiators for the purposes of heat dissipation & volume though. I still think you will be fine even if you exclude the bedroom rads.

The advantage of oversized bedroom radiators is that if you want those rooms to warm up in the morning (after a night-time set back for example) then they will do so quickly.

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Thanks.

I suppose there is no ā€œperfectā€ sizing of the system and you also have to work with the installers guidelines to a degree. I think BG have done a decent job so far, which was a significant improvement on Octopus.

I hadnā€™t considered quicker recovery times in the early morning with having slightly bigger radiators in the bedrooms, which should be a benefit.

Iā€™m not chasing the best COP possible, as that will have diminishing returns on ROI, especially I have 45kwh of battery storage. The BG install is very good value, many, many thousands lower than the Heat Geek install I was quoted. Iā€™d never recover the upfront cost.

Iā€™m confident Iā€™ll have a plenty warm house, I just donā€™t want too much cycling by oversizing our radiators unnecessarily

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Iā€™ve also been testing again our Vaillant system boiler at 45c flow rate. It works well, modulating quite low and running for long periods, although with cold spots where the existing radiators arenā€™t big enough.

Iā€™ve hooked up a power meter to the boiler and it draws 110w and only ever reduces down 80w at best, which is quite a chunk towards the 300w or so draw of the 8kw Daikin when its ticking along.

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Indeed. Especially where Government grants are involved, the design is (rightly) considering future owners of the building who might have different requirements from you, needing higher (bed)room temperatures.

If anything, youā€™ll get less cycling with bigger radiators - provided the TRVs are open. If you find the bedrooms get too warm you can use the TRVs to reduce their output slightly, which is little different from having smaller radiators in the first place.

It does sound as if BG have designed you a decent system.

Iā€™m fortunate to live in a Passivhaus so I have the ā€œproblemā€ that all the rooms are the same temperature as each other, within a degree or so. The bedrooms have no direct heating but theyā€™re generally 20 - 21C all the time, and itā€™s fine; the main adjustment I needed to make was to do away with the winter duvet.

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Thanks.

With TRVs I assumed they just close off completely when the room gets to the desired set maximum temperature.

Do they in fact reduce the flow and at which point do they shut off completely?

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I guess ā€˜smartā€™ TRVs (with batteries and a digital display) might do something fancy like cycling completely on-and-off every few minutes, but old-school TRVs just have a wax capsule which expands and contracts, pushing on the valve pin. Those will partially close the valve, allowing through just enough flow to maintain the room temperature. They should only close completely if the room gets significantly over-temperature (e.g. due to passive solar gain).

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Manual TRVs typically have a range of approx. 2C over which they gradually reduce the flow. Below that they will be fully open, above it fully closed.

Smart TRVs in theory can implement more complex logic, but in reality appear to do something very similar to a manual TRV. Iā€™d say both are roughly equivalent in terms of getting to a temperature and holding it.

The advantage of a smart TRV is the ability to set a schedule, so a different temperature set point at different times. This could allow you to raise the bedroom temperature an hour before you get up, and then drop it back down through the day.

The disadvantage of a smart TRV in a bedroom is that they make a little bit of noise when the room temperature is close to the set-point. The valve is controlled by a solenoid which can be heard as it alters the valve position. A manual TRV by contrast is silent.

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Excellent, the BG system sounds good.

Knowing the cold spots with heat-pump type flow temperatures is hugely useful. Make sure your new radiator sizing schedule takes account of these (bigger radiators relatively for the areas which are currently the cold spots). This type of real-world data trumps the theoretical models of a heat loss survey, even if that survey was done in a lot of detail.

The fact that gas heating systems have an electrical consumption is almost always ignored when comparing the cost to a heat pump with COP 3-4. As you correctly point out the gas systems electrical usage is not insubstantial. Just so you arenā€™t disappointed the small Daikins will run down to 300w in the right conditions (low flow temp and fairly high outside temp) but 400w is a more realistic floor during the bulk of heating season. YMMV depending where in the UK you are.

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Agree!

We also had 3 water pumps with the boiler / Polypipe system.

1 for the boiler circuit and 1 for each UFH manifold.

When running they used about 50W each.

Reckoned to cost upto 2 x Ā£48 extra a year!

These also had a short run cycle once a day, everyday of the year, to prevent seizure during the summer months of UFH inactivity.

The UFH manifold was simplified as the Daikin has a pump capable of doing the whole thing.

The Polypipe system had 6 thermostat zones all wired. These push/pulled the temperature around and it was never where we wanted it.

With the Heat pump itā€™s a very consistent temp throughout the whole house and annexe now.

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We knew our cold spots from running the boiler at 45c last winter. The good thing is that BGā€™s survey picked this up with the heat loss calculation and were spot on with the sizing of those areas, which was reassuring.

They just designed the bedrooms at 21c when others were at 18c which we werenā€™t expecting.

We are not unhappy with that, as weā€™ve ended up with slightly bigger bedroom radiators without paying any extra, although they may require a little managing to keep them from overheating.

Their heat loss survey was excellent (as well as their engineer of 25yrs experience), using lidar technology and a proper chat around the house and extension construction materials.

In the report we even had a lovely floor plan of the entire house to the mm, including cupboards and everything (along with many other pages of detailed calculations).

Hopefully their install will be as good as the survey.