ECODAN , can I run just the heating without DHW?

MultiFuelBurner

Just see how it goes and it's good you have photographic evidence and then you can save those off and how it went.

It is a bit like running a science experiment 

Swizz

So, I've been running with WC since Monday. It is an interesting experiment. Our daily consumption is around 15/17kwh
Because of the woodburner it does seem to turn itself off as thermostat in lounge limiting it for around 4 hours, also, we have massive solar gain from our south facing open plan upstairs living space..
I'm not sure if that consumption is reasonable given the outdoor temp around 8⁰ in the non sunny areas..
I've got the WC set at 35⁰ for -3, and at 25⁰ for 13⁰
Do you think all this sounds reasonable . The cop is only about 2

matt_drummer

How big is your house?

What is the heat loss?

How big are your radiators?

If you are currently running your flow temperature at around 30c your radiators will need to be huge to deliver the heat produced by the heat pump.

I would assume they are not big enough to do this looking at your COP.

If a radiator is designed to deliver 1,000 watts of heat @ at a dt of 50c it will only deliver about 100 watts at those low flow temperatures.

If your radiators cannot deliver the heat produced by your heat pump you will find the efficiency is terrible.

Your heat pump will have a minimum amount of electrical input it can run at and therefore a minimum heat output related to the COP. If the minimum electrical input is 500w and the COP is 2 then you get 1,000w of heat, at a COP of 5 you would get 2,500w of heat.

If your radiators can only deliver 1,000w of heat at a flow temperature of 30c then that would give you a COP of 2.

To get the best out of your heat pump you need to find out what is going on, reducing flow temperatures below what the system can handle will cost you efficiency and money. You may find it cheaper to run higher flow temperatures.

Without any data though it is all guesswork.

Go and have a look at how radiator output falls as the difference between the mean flow temperature and room temperature closes.

https://www.radiatorsdirect.co.uk/delta-t-conversion

Your COP at those sort of outside temperatures should be somewhere between 3.5 and 5.0

Have a look here,

https://heatpumpmonitor.org/system/list/public

You will be able to see what similar heat pumps to yours can do.

Swizz

I set the WC at a level suggested on an ecodan YouTube video. Our radiators were all changed when system was installed. Surely if it's running on WC , then ghd flow temperature is just a fact, as it's not attempting to reach any set temp in the room. We actually find it very pleasant at those temperatures.
If I were to increase the upper and lower parameters, that would just make the radiators a bit warmer ..or should i be setting the room temp and increasing flow temperature and still use WC
Getting quite confused ..

Reed_Richards

Swizz said:

I've got the WC set at 35⁰ for -3, and at 25⁰ for 13⁰
Do you think all this sounds reasonable . The cop is only about 2

My heat pump was designed for a flow temperature of 50⁰C when the outside temperature is -3.8⁰C.  So the lower end of my WC line is 50⁰C for -4⁰C outside.  That should apply to any heat pump, the lower end of the WC line should correspond to the design parameters, although you might subsequently find you need to modify this if the calculations used for the design were a bit out.

My upper parameters are 29⁰C at 18⁰C outside.  This is based on radiator output calculations (I have only radiators) to give a good fit at lower temperatures.  Towards the top end of the outside temperature range this gives me output water that is a bit warmer than necessary, but the best I can do fitting a straight line to what is actually a curve.    

matt_drummer

Swizz said:

I set the WC at a level suggested on an ecodan YouTube video. Our radiators were all changed when system was installed. Surely if it's running on WC , then ghd flow temperature is just a fact, as it's not attempting to reach any set temp in the room. We actually find it very pleasant at those temperatures.
If I were to increase the upper and lower parameters, that would just make the radiators a bit warmer ..or should i be setting the room temp and increasing flow temperature and still use WC
Getting quite confused ..

Whilst running at those flow temperatures you may find your house gets warm enough.

But it may not be the most efficient way to run it.

I have electricity meters and a billing grade heat meter fitted. 

I can heat my house quite easily to 22c at a 30c flow when it is 7c outside.

Sounds great doesn't it? Should be really cheap to run, cheaper than running hotter.

But when you look at my data it uses more electricity overall to run at 30c than it does at a higher temperature.

My heat pump short cycles and my radiators are not big enough to provide all of the heat generated by the heat pump. Every heat pump has a minimum heat output, if it can't deliver it through the emitters, in your case radiators, than that heat gets wasted. You are consuming electricity and producing no heat in your home with it.

It ends up costing more to provide less heat.

You can only really look at it in this detail if you have monitoring equipment.


But, whatever your views and knowledge a COP 2 is awful.


I don't know your house but I am pretty confident that your radiators cannot cope with a flow temperature of 30c.


Your COP should be between 3.5 and 5 realistically depending on the quality of your installation.


You really need to do some research and reading.


People who tell you that low flow temperatures are best and save you money are correct in theory but it only works if your system is designed for it.

People who tell you that it works for them need to back it up with data, it cannot be based on a gut feeling because everybody will think that heating water to a lower temperature must be cheaper, that is not the case with a heat pump unless everything is designed to work like that.

Swizz

I am doing my best to research, but I'm finding so  many conflicting articles. Ones from other forums where people are saying you need the lowest flow temperatures you can manage. I find it hard to get my head around the idea that I should be heating the water hotter for the radiators. We've turned the HW off

Reed_Richards

All else being equal the hotter you make the water leaving your heat pump then the more energy is required so if you can heat your house effectively with a colder output flow that should be more energy efficient.  Hotter radiators will heat your house faster so if you have a room thermostat that switches off the heat pump when it reaches the set temperature then that will happen faster so your heat pump should operate with shorter cycles.

What could go wrong?  I guess if it turns out that the water temperature you are asking for is so low that even the minimum output of your heat pump will cause that temperature to be exceeded then your heat pump will get itself in a mess and will run in very short cycles.  Usually under those conditions your house just won't get warm enough so you know something is wrong.  But if it's warm enough outside there could still be enough heat from the radiators to reach your desired temperature.  So you would have to set an upper limit to your WC line to prevent this.

Now in my case my heat pump is not allowed to short cycle, the minimum allowed cycle time is 20 minutes.  I don't have any energy monitoring equipment so I don't know what my COP is.  If you can measure COP then I guess the thing to do is experiment with the upper limit set on your WC line and see if that has any effect on your COP when it's mild out.    

matt_drummer

Swizz said:

I am doing my best to research, but I'm finding so  many conflicting articles. Ones from other forums where people are saying you need the lowest flow temperatures you can manage. I find it hard to get my head around the idea that I should be heating the water hotter for the radiators. We've turned the HW off

You are running at very low flow temperatures and getting a COP of 2, that obviously does not fit with the idea that low flow temperatures are most efficient, they are if the whole system is capable of it, I don't think most are, mine cannot do it as its is.

If you are happy with that then leave it alone.

If you think a COP of 2 is not very good or you would like to improve it then you will need to make some changes.

As lower flow temperatures use less electricity then the only way to use less is lower the flow temperature even more.

The COP is just the relationship between the heat produced and the energy used to get it.

On any given day your house will require a certain amount of heat to maintain the internal temperature.

Let's say that it is 7c outside and you want to be 20c indoors for the whole day and that will require 48kWh of heat to do this, that's 2kW an hour.

So you could run your heat pump continuously for 24 hours putting 2Kw an hour into the house. You do this at a flow of 30c and the minimum electrical input of the heat pump is 1kW. This will use 24kWh of electricity at a COP of 2.0

But, your heat pump should really be producing 4Kw of heat at 1kW input and 30c flow, you are losing 2kW of heat every hour as your radiators cannot deliver what the heat pump is producing or should have been producing. The heat pump is not linear in its heat output, it varies and is affected by different factors.

I'll try another way, your house calls for heat so the heat pump starts running drawing 1kW of power. It should be putting 4kW of heat into your house but the house cannot take it as the radiators are at the limit of what they can deliver to the house at the low flow temperature set. The house can only take 2kWh of heat so that is what the heat pump produces even though it could be producing 4kW of heat. But this is the killer, it still draws 1kW of electrical power because that is the lowest amount it needs to operate.

So what you could do instead is run at a flow temperature the radiators can handle.

To get 48kWh of heat into the the house you could turn the flow up to 40c. The heat pump now needs 1.2kW of electrical power as the flow temperature has gone up but it is now able to produce 4kW of heat as the radiators can deliver the full heat produced to the house as their performance/capacity improves the bigger the difference between the flow temperature and the room temperature.

As you are producing 4kW of heat an hour the heat pump now only needs to run for 12 hours to produce the 48kWh of heat required.

This means you will have used 15kWh of electricity to produce 48kWh of heat so your COP is now 3.20 instead of 24kWh of electricity at a COP of 2.0


That is how running at a higher flow temperature will produce better efficiency.

It cost more to heat the water more but it produced more heat and and had to run for less time meaning you used less electricity overall for the same result.

This is how it is when you need the minimum output from your heat pump, once it is really cold it behaves just as you expect, lower flow temperatures cost less
.
The size of this problem depends on your heat pump, your house and how well matched they are.

You are getting a COP of 2, its not good, can you not talk to your installer?

matt_drummer

Here is my real life example.

I have a 9kW Daikin heat pump. It's minimum electrical input is 920w, it cannot consume any less electricity.

At a flow temperature of 35c it should achieve a COP of 5.0 producing 4,600w of heat

My radiators can deliver 8,893w of heat at a flow of 50c and a room temperature of 20c, that is a delta t of 30c

At a flow of 35c my delta t falls to 15c and my radiators can now only deliver around 3,000w of heat

So when I try to run at 35c my heat pump consumes 920w of electricity (its minimum) but only delivers 3,000w of heat. The COP is now only 3.26, not the possible 5.0.

This is all because my radiators are not big enough to handle the heat produced at that flow temperature

A few weeks ago I ran the heat pump on a WD curve with a flow of between 28c and 31c during the day. The heat pump ran in shorter cycles but nothing terrible and my house was warm enough at 22c when it was 7c outside. You would think that would be really efficient, in terms of COP it was terrible, in terms of electricity consumption it may actually have been better than my latest attempts. COP isn't everything, using the least of amount of electricity to heat your house it what matters.

If I want more heat I have to increase the flow temperature and that uses more electricity.

But my house needs less than 2kW of heat in these conditions.

My heat pump is too big in these circumstances and is actually too big in all circumstances for my house.

I could increase my radiator sizes, they are already big but they need to double.

If I wanted to run at 30c flow then it would be even worse, my radiators can only put out less than 2kW of heat at a delta t of 10, my COP would fall below 2.0 as my heat pump cannot use any less electricity.

My problem is also compounded by the fact that although I only want the house to be 20c I have to let it get hotter if I want the heat pump to run for longer periods.

A hotter house reduces the delta t (the difference between the flow and room temperatures reduces) and the lower delta t reduces radiator output even more making the heat pump produce less heat and therefore losing efficiency.

This carries on until the heat pump shuts down through not having anywhere to send heat to. It cools down and then tries again and so on.

If I increase my radiator sizes then my heat pump will be able to produce all the heat it wants to at the low flow and minimum electrical input.

That's great but I will then be dumping 4,600w of heat into a house that needs less than 2,000w. The house will either get hotter or the heat pump has to run less.

Running the house hotter will just be uncomfortable and running the heat pump in shorter bursts is inefficient as the initial energy consumption to get running each time is a lot.

I will never get the best out of this heat pump in this house even if I double my radiators sizes. The only way to make it work would be to increase the heat loss of the house.

I hope you can see from my real life situation how a low flow temperature is not reducing my electricity consumption and does not return the best COP from my heat pump.

I hope that you don't have a situation like me but trying to run really low flow temperatures through radiators is not as straightforward as it sounds.

I have detailed monitoring on my system and anybody without something like this is just guessing as to what is going on. Low flow temperatures sound like they must be the most efficient, it sounds logical, but you need all the data to find out what is efficient and what is not.

Just run your heat pump to get the house comfortable, keep a record of the weather conditions, electricity consumed and heat produced if you have it and then make small changes over time to find the best for you and your house.

It will take time and maybe cost you extra electricity some days but just think of that as part of the capital cost.

You will find a base setting that works most days that you can then fine tune as time goes by and your experience builds.

You can look at my heat pump here and see how badly it is performing. Mine is the Octopus installation in Ipswich.

HeatpumpMonitor.org

You will see clearly the minimum electrical  input, the flow temperatures, the heat produced plus the internal and external temperatures whilst it is doing it.

Then look at others, especially ones similar to yours and you will be able to see what is possible and get ideas on how to run your heat pump.


I just thought of one more way to help make it clear

In 10 hours my house needs 20kWh of heat

I can run at 35c and my radiators put out a maximum of 2kW an hour at that flow temperature and I used 920w an hour of electricity so I used 9.8kWh of electricity to heat my house.

At a flow of 45c and my radiators put out 4kW an hour and my heat pump is now using 1.4kW an hour of electricity but only needs to run for 5 hours. So I have used 7kWh of electricity to produce the 20kWh of heat I needed.

I used 2.8kWh less of electricity to produce the same result because of the limitations of the heat pump and the radiators.

It was cheaper to run at a higher flow temperature even though all logic suggests the opposite would be true.