OK Terry, thanks.
You should easily get 8kW of heat from your heat pump with those radiators..
At 40c flow, 20c room temperature your dT should easily get to 10c and require a flow rate in excess of 7lpm to control it.
Why aren’t you?
Where’s your data for us to look at?
Do you have trvs fitted Terry?
Yes,single zone and the trvs are fully open and never touched. Not sure what data you want, I don’t have the measurement tools fitted. And I agree I should get the 8kw, but the system doesn’t go beyond 4.88kw, at best!! But I said that already. So what data do you want to help unravel the mystery?
Hi Terry,
Where do you get all your figures from?
Please don’t say the MMI.
Do you know how the central heating pipe work in the walls is setup, and what size it is? If you’re not able to get the heat transferred with that much emitter capacity available, it suggests there’s a bottleneck elsewhere in the system.
@matt-drummer . MMI! So I use the total figures and then calculate the usage from last set of total figures to latest set. Daikin tell me that the total figures don’t have the issues of the daily and hourly figures. Then I have all my data from my smart meter, so I can confirm what my usage in total has been and compare that to how much the heat pump has taken. In the winter typically I was using a max of 2kwh for things other than the heatpump. And the numbers matched closely. So I could see how much I was inputting and then getting the output figures from the MMI. As I was getting fairly consistent numbers around 4 for cop heating and 2 for DHW that seemed about right. At max during the coldest days I was running at about 20kwh input. So a little less than 1kwh per hour and from this I was getting around 4kwh output. So I could see that I was getting stymied somewhere. Esp given that on those cold days my lounge was running at about 13c. So the radiators had bags of capacity ( and this was on 45c flow temp) but insufficient input. Subsequently I found out the physics behind it, which tells us that dT *flow rate gives us the output of the heatpump.
OK.
It’s difficult to see what is going on.
You will have defrosts and all sorts to contend with so using averages whilst helpful is vague.
A COP of 4 on the coldest day is optimistic to say the least, especially at 45c. I don’t get that at 30c on the coldest days.
When your lounge is at 13c what’s the rest of the house like?
Are your radiators actually hot?
Does it feel like a 45c flow temperature?
Have you been able to measure the actual water temperature in an out of each radiator?
Something is wrong.
I was also just thinking, how do you run a three bedroomed house on less than 2kWh a day?
That is no more than 83W of power on average!
Answering your last question , by careful control of what I use. My base load was 43 watts, basically that’s my router and whatever power is being taken by the various controllers for the heat pump and cylinder and the clock on the oven. I never leave anything on standby. As I’m looking at my smart meter now I can see my current consumption is 47watts. Things are powered up only when needed. My total power consumption is around 60kwh per month, unless I have visitors, July was 100kwh, I had visitors. Also I had no fridge or freezer which can be big consumers of power. I do now have a small refrigerator that does now add to the baseline, but it’s very low, when it kicks in it might push up consumption by 30 watts, but it’s not on for long. I don’t like waste. I am mindful of the resources I am using.
I’m assuming you have an EDLA08. Where are you looking for the setting meanings? I’m looking in the Installer Reference Manual. The Field Settings section doesn’t have any explanations other than in that manual, it’s just magic numbers entered against identifiers displayed in a matrix.
You could always consider installing ESPAltherma, which is a cheap way to get continuous data from the HP, which, while not up to MID standards, provides comparative data over time. This is extremely useful when making changes, to observe the effects.
Finally, did you ask Octopus or whoever installed it? I’ve found them, and Daikin, extremely helpful and willing to work to solve my problems. In fact, if your system isn’t doing what they said it would, they have to fix it as part of the MCS deal. Ah, you did already - “I recently had Daikin and supplier looking at that and they confirmed they were ok.”
Hi Terry,
In answer to your original question I have the 6kW Daikin. Mine is capable of and does output its full specified output power, or near enough. However it doesn’t do it very often because there is rarely the demand put upon it. As a basis for comparison the 3 bedroom house (80m2) in Scotland I live in has had a maximum heat requirement of 3kW when it was -8C at night rising to -2C in the day.
My gut feel is that the situation is the same for you. The heatpump (and I mean specifically the heatpump, not the whole heating system) is not being asked for 8kW of heat, and therefore it doesn’t produce it.
Lets forget all the technical stuff and return to the basics. What is the actual problem you are trying to solve? I assume that it is that your house is not kept warm when its cold outside. You mentioned in one post that the lounge stay at 13C. This is clearly not a heating system working properly. Can you give full details of what the problem is (whole house, specific rooms, all the time, only when cold out, etc)?
Here’s the technical bit to try and explain, as Ben & Matt have, about what is going on. But I think the answer lies above in the fundamental problem rather than what the heat pump is doing.
You are correct that a combination of a 10C difference between LWT and RWT combined with 7Lpm flow rate equates to ~4.9kW of heat. However, lets be clear about the settings, in selecting radiator in the Daikin MMI you have asked the heat pump to target a LWT/RWT of 10C. However there’s no setting that says use 7Lpm flow rate, that is being selected by the Daikin control algorithm.
You allude to the fact it is higher before it reaches steady state, which is what I would expect. The low flow rate is being selected because not enough heat is being dissipated by the radiators to warrant a higher flow rate. So the situation is back to front from what you suggested. Its not that a 10C difference & 7Lpm implies in a 4.9kW limit its that a targeted 10C difference combined with 4.9kW demand implies a flow rate of 7Lpm.
Its also worth noting that 7Lpm is the lowest flow rate the 4-8kW Daikins will flow at. At heat demand of less than 4.9kW the flow rate will stay at 7Lpm and the difference between LWT and RWT will drop below 10C (this is that state that my heat pump spends most of its time in).
You mention the Daikin spec of 12Lpm minimum of flow for the radiator circuit. This is correct, the specification for the heat pump requires a minimum possible flow rate (at maximum pump speed) of 12Lpm round the radiator circuit. It doesn’t mean that this is the minimum flow rate that the heat pump will choose. The fact you are seeing 7Lpm is normal. If you start the system from cold, I’d expect that you would see more like 15Lpm flowing until such time as LWT rises to your desired temperature.
I doubt there is anything wrong with your heatpump, but if your living room only gets to 13C there is definitely something wrong with your heating system. Your radiators look plenty big enough, my guess is that the problem lies in the pipework.
Finally, if you want to confirm that your heatpump is capable of producing 8kW for heating you can do the following. Let the water in the system get cold (turn the heating off for a couple of hours). Turn the heating on. In the MMI Information screen watch the LWT, RWT and Flow rate. From the instantaneous values of these three you can calculate the heat being produced. As a rule of thumb at 15Lpm each degree of difference between LWT and RWT is 1kW of heat. At 7Lpm its about 0.5kW for each degree of difference. As your system heats up the water in the heating system you should see it producing in the region of 8kW. I’d expect to see for example LWT 34, RWT 26, Flow 15Lpm. You’ll see it maintain roughly 8kW up until it reaches your desired LWT.
I was reading this Heat Geek article: Heat Pump Piping: Do You Really Need to Upgrade Your Pipes? - given that Terry has said there’s no longer a buffer tank in the system is it possible that, with the heat pump unable to raise the DT much above 5-7, there could be a severe restriction somewhere in the pipe work?
I wonder because my read of the article suggests that if either the main central heating ring is 15mm or there are large radiators being fed by 8mm microbore then perhaps enough heat simply can’t reach the radiators?
I don’t know how this would present in practise though, would the radiators be colder than expected?
@John , still can’t find that in my manual, we appear to have different versions. And I can’t find it in the settings even using the installer code. Guess it’s hiding somewhere. What is yours set to?
Mine is set to 0, no limitation. To be honest, I wouldn’t expect anyone to have any other setting generally, especially if installed by someone like Octopus, who have a pretty canned setup. To quote the manual
Pump speed limitation [9‑0D] defines the maximum pump speed. In normal conditions, the default setting should NOT be modified.
In respect of the manuals, the link in my previous post directly accesses the manual I’m using. Which manual are you looking at? It’s not in the User Manual, or the Installation manual. You have to look in the Installer Reference Guide.
That manual also explains how to find the field settings:
But quite honestly, if pros have looked at your system in person, and haven’t spotted that, given the improbability of it being modified, I can’t see that being the difficulty. As @Jonathan says, what temperature are the radiators at during the cold weather, especially if the living room is 13C? That’s a fundamental clue… if the pump is producing water at 45C, then the radiator will definitely feel warm to touch, all over.
You could jack everything up now, set LWT to 50C, thermostat to max, and see if rads are the same temp, and how long it takes for them all to reach the same temp. Might be worth getting an infrared thermometer gun, really handy for checking this and lots of other stuff (non-Amazon sources also available!).
I’m thinking the same as @John. I’m going to take a guess at the underlying problem, there isn’t enough water getting to the living room, dining room and kitchen back radiators which are huge radiators according to the Octopus schedule.
Do this, and see if all of the radiators get warm all over.
My guess is going to be that the landing, loo, hallway, bedroom 2/3 and kitchen front ones do but the kitchen back, living room and dining room ones are warm at one end and cool/cold at the other.