ASHP flow temperatures in winter

[Orion331]

Hi,

 

I've recently had an ASHP installed (Mitsubishi Ecodan Monobloc 8.5kw) and have found since it's install in July there have been no issues with it. However, since November where temperatures outside have dropped below double digits, I am unable to get a single part of the house up to 21 degrees even when the flow temperature is set to 55 degrees for 24 hours.

 

I have contacted the installer and explained this but they are advising me that I need to run the heat pump at max during the colder months. I don't feel this is correct and that the issue may be that the radiators in my house aren't correct sizing, even though they inform me they "should be okay if the flow temperature is at least 55 degrees. 

 

This is costing me lots of money in energy bills when we were sold this as a cheaper alternative to heating our home.

 

Any advice would be great!

[Orion331]

Hi,

 

I've recently had an ASHP installed (Mitsubishi Ecodan Monobloc 8.5kw) and have found since it's install in July there have been no issues with it. However, since November where temperatures outside have dropped below double digits, I am unable to get a single part of the house up to 21 degrees even when the flow temperature is set to 55 degrees for 24 hours.

 

I have contacted the installer and explained this but they are advising me that I need to run the heat pump at max during the colder months. I don't feel this is correct and that the issue may be that the radiators in my house aren't correct sizing, even though they inform me they "should be okay if the flow temperature is at least 55 degrees. 

 

This is costing me lots of money in energy bills when we were sold this as a cheaper alternative to heating our home.

 

Any advice would be great!

[ProDave]

More details please, house type, age, insulation levels, and what heating was there befoer.

 

3 minutes ago, Orion331 said:

when we were sold this as a cheaper alternative to heating our home.

 

Cheaper than what?

 

Don't forget temperatures now are probably colder than you have had for a very long time, especially down south.

[Orion331]

It's a detached 4 bedroom house, new build (Feb 2022) and insulted very well above building regs. The original heating was an oil boiler.

 

The company that designed the original heating system with the oil boiler are telling me the radiator output isn't good enough for the house where as the ASHP installer are telling me it's fine as long as your flow temps are 50+ degrees.

 

[Orion331]

It's a detached 4 bedroom house, new build (Feb 2022) and insulted very well above building regs. The original heating was an oil boiler.

 

The company that designed the original heating system with the oil boiler are telling me the radiator output isn't good enough for the house where as the ASHP installer are telling me it's fine as long as your flow temps are 50+ degrees.

[ProDave]

It sounds like your ASHP installer has badly misled you.

 

Perversely at the moment, it seems oil has gone up in price in the present cost of living crises less than gas and electricity has.

 

But if you have been "sold" an ashp that only works properly if the radiators are ran at over 50 degrees, then that is a poor install.  Unlike other heat sources ASHP's work best with low temperature water, so that usually means under floor heating or larger low temperature radiators.

 

Even with everything just right, an ASHP will just about match the cost of for instance mains gas. They are not a magic cheaper form of heating, anyone telling you that is somewhere between optimistic and fraudulent.  they do have environmental benefits, less CO2 emissions.

[Orion331]

It seems when I asked them if the radiators will need upgrading, they have lied to me completely.

 

I'll have to take this up with them as it's immensely expensive running at 50+ and not getting the rooms to a comfortable temperature in the process.

 

Thank you for your advice!

[Kelvin]

Out of curiosity if it’s a new house built with an oil fired boiler why have you changed it to an ASHP so soon? 
 

In any event, you can’t just swap an oil/gas boiler for an ASHP and leave everything else the same. ASHPs operate most effectively at lower temps pumping the heat into a large surface area hence why under floor heating and a big concrete slab works really well. It’s harder to replicate this with rads but you can get much bigger rads or fit an ASHP that runs at a higher temp. Personally I don’t think I’d fit an ASHP into a house without UFH for at least the downstairs. 

[Orion331]

The aim was to make the house as green as possible and stop relying on things like oil especially as we were expecting the oil cost to rise. We weren't expecting a magic cheap source, just one that cost around the same but worked and it doesn't even provide anywhere near the warmth we need in the house.

 

The company that installed our ASHP provided advice on what we'd need and recommended the radiators weren't changed. Now we're left with a heating system that doesn't heat the house and we've got no choice but to upgrade the radiators.

 

 

[ProDave]

6 minutes ago, Kelvin said:

In any event, you can’t just swap an oil/gas boiler for an ASHP and leave everything else the same. ASHPs operate most effectively at lower temps pumping the heat into a large surface area hence why under floor heating and a big concrete slab works really well. It’s harder to replicate this with rads but you can get much bigger rads or fit an ASHP that runs at a higher temp. Personally I don’t think I’d fit an ASHP into a house without UFH for at least the downstairs. 

Millions of people will learn this lesson the hard way, if the government gets their way and people do start en-mass swapping gas boilers for ASHP's with nothing else being done.

[ProDave]

4 minutes ago, Orion331 said:

The company that installed our ASHP provided advice on what we'd need and recommended the radiators weren't changed. Now we're left with a heating system that doesn't heat the house and we've got no choice but to upgrade the radiators.

Go back to the company and say their advice was wrong.  Was this funded by any sort of grant?

 

If they won't admit they got it wrong, try trading standards.

 

The ambition go go green is good, it is just a shame you have so far had bad advice from an installer.

[Orion331]

Yes it was 50% funded by a government grant.

 

I'll take it up with them, otherwise if no resolution can be found I'll have to take it further like you said.

 

Gutted we found out the hard way unfortunately.... it's going to be a cold and expensive winter.

[Kelvin]

This week has been particularly cold so a real test for your system. Milder weather is due next week. 
 

We rent a farmhouse with no cavity wall insulation. Even with the oil fired boiler on all day the peak temp in the house is 15^oC. The only room we can get it higher is the living room which has a wood burning stove. It’s so cold in the kitchen all the olive oil solidified 😂 🥶 

[ProDave]

Do let us know what they say.

 

I am a big fan of ASHP's used correctly but deeply sceptical about the plans to replace most gas boilers with an ASHP as I fear the vast majority are going to end up like this performing badly, and the resulting bad press will have everyone claiming ASHP's are rubbish. 

[ProDave]

1 minute ago, Kelvin said:

We rent a farmhouse with no cavity wall insulation. Even with the oil fired boiler on all day the peak temp in the house is 15^oC. The only room we can get it higher is the living room which has a wood burning stove. It’s so cold in the kitchen all the olive oil solidified 😂 🥶 

Yes but the OP has a less than 1 year old new build.  We would hope that is built better, but perhaps that is another can of worms?

[Orion331]

I feel for you not having good insulation, I'm losing my mind over a couple of degrees 🤣

 

I will keep you updated, can't imagine it's going to be an easy process.

 

I do believe the heating system would work great if the radiators were correct.

 

Hindsight is a wonderful thing.

[Orion331]

I've been through the build and insulation of the house and there are zero issues with that thankfully.

 

I believe this issue is just getting the heat into the rooms via the radiators.

 

[Bozza]

I feel sorry for you.  Just one thing to consider.  My ASHP system, also Ecodan, where there is demand for both hot water & heating at same time, will default to hot water.  Is yours the same? 

 

Is your system seeking demand for both hot water and space heat at the same time?

 

My system is set up so the ASHP will generate HW into the tank late morning, on the ASHP timer.   The ASHP is on a constant run otherwise, but only actually runs when the space heating thermostat demands it around its own timer being on, If that makes sense.  So the only runs when it demands actual heat to the required room temperature.   So the HW is only generated at a time when the ASHP is not being used to generate heat for the central heating.

 

Just ruling out your settings are ok and ASHP is not trying to heat water & space heat at same time.  

 

 

 

 

Edited December 15, 2022 by Bozza

[joth]

1 hour ago, Orion331 said:

Yes it was 50% funded by a government grant

In this case it must have been an MCS install so follow the complaints steps on

https://mcscertified.com/complaints-compliance/

 

Even before you get MCS involved, you should follow their steps and ensure you have record of the complaint to the installer etc

Edited December 15, 2022 by joth

[Bramco]

20 minutes ago, Bozza said:

My system is set up so the ASHP will generate HW into the tank late morning, on the ASHP timer.   The ASHP is on a constant run otherwise, but only actually runs when the space heating thermostat demands it around its own timer being on, If that makes sense.  So the only runs when it demands actual heat to the required room temperature.   So the HW is only generated at a time when the ASHP is not being used to generate heat for the central heating.

 

We're on Octopus Go, so have the ASHP on for 4 hours at the cheap rate and then a few hours late afternoon.  If we used the ASHP to heat the hot water, it would be at the more expensive rate, about 32p if I remember correctly.  But the cheap rate is only 7p, so we have the hot water heated on a timer at the cheap rate - that's until we install the solar PV - although that wouldn't have been much use here for most of the last 10 days, way too dull.

 

So if you can heat your hot water via the immersion, you will free up time that the ASHP can be doing just heating, rather than switching between the heating and hot water.

 

Simon

[Bozza]

27 minutes ago, Bramco said:

 

We're on Octopus Go, so have the ASHP on for 4 hours at the cheap rate and then a few hours late afternoon.  If we used the ASHP to heat the hot water, it would be at the more expensive rate, about 32p if I remember correctly.  But the cheap rate is only 7p, so we have the hot water heated on a timer at the cheap rate - that's until we install the solar PV - although that wouldn't have been much use here for most of the last 10 days, way too dull.

 

So if you can heat your hot water via the immersion, you will free up time that the ASHP can be doing just heating, rather than switching between the heating and hot water.

 

Simon

Surely using the immersion to heat water uses more KW than the ASHP? And thus more expensive on a non variable rate.?  That’s what I’ve always been told.  Certainly my installer advised me to use the immersion purely as an emergency back up should the ASHP break?  Or am I missing something?    
 

in our case having the ASHP heat water for a few hours late morning is not a problem as we retain existing warmth from the heating being on before that , plus solar gain we bet from being south facing?  Obviously if using the immersion is cheaper that using ASHP but like I said difficulty in understanding how that could possibly be?

 

 

[ReedRichards]

I replaced an oil boiler with an ASHP and I am very satisfied with the result.  But almost all of my radiators were replaced with ones having a much larger output and two new radiators were added where there wasn't room for a bigger radiator.  You were badly misled when advised that you did not need to replace your radiators and equally misled that running a heat pump at 55 C or more is a good idea.    

[Orion331]

The settings on my heat pump are all correct and the water heating is not happening at the same time.

 

After reading all your responses, I am confident that I have been misled. I am more frustrated that they are trying to convince me to run the heat pump at 55 degrees or more just to make up for their failure.

 

I have contacted them to complain about the issue and will update when I receive a response. 

 

In case you are all interested, the company I used is called Rural and Country Energy.

[Dave C]

6 hours ago, Bozza said:

Surely using the immersion to heat water uses more KW than the ASHP? And thus more expensive on a non variable rate.?  That’s what I’ve always been told.  Certainly my installer advised me to use the immersion purely as an emergency back up should the ASHP break?  Or am I missing something?

 

The idea would be:

-Off peak rates are 1/4 of peak time on Octopus Go (or maybe even less - more like 1/5 for me)

-If your heat pump has a COP of <4, it's cheaper to use the immersion off peak than to use the heat pump during peak time

-Obviously during a time of year when you don't need heating, you just run the heat pump to heat up the hot water tank. But when it's cold enough the heat pump is working a significant portion of the day to keep the house warm, you could be better off running the heat pump on space heating for the entire off peak period, and simultaneously running the immersion to deliver hot water.

 

The immersion is less efficient - but it's cheaper than running the heat pump for 2 off peak hours on hot water and then having to run the heat pump for 2 hours more during peak time.

 

Only makes sense on Octopus Go like plans, though, where the off peak rate is so cheap it outweights the COP advantage of the heat pump. As you said, on a non-variable rate, you wouldn't use the immersion at all.

[HughF]

It's all about flow temp and rad sizing, always.... Take a look at Glyn Hudson's performance data from this cold snap, rads sized for 35 deg flow:

 

http://emoncms.org/samsung5kw/app/view?name=Samsung5kWASHP

 

Consistent COP above 3...

 

The cowboys who did your system design just go to show how incompetent most people in this industry are. I could do a better job from my armchair having watched some youtube...

Edited December 16, 2022 by HughF