Heat pump quote

Alnat1

Octopus are fine with microbore for radiators up to 1kW but ask you to repipe on copper before the install if any need to be bigger.

Our living room radiator is on an internal wall that backs onto the integral garage, where the gas boiler was, and it needed to be over 1kW. Octopus sent one of their guys round for a look and he said it could be piped off the boiler in and out pipes once it was removed during install.  They do try and get around any problems with minimum disruption if at all possible.

70sbudgie

Alnat1 said:

Octopus are fine with microbore for radiators up to 1kW but ask you to repipe on copper before the install if any need to be bigger.

I am starting to think that I have mis understood what microbore pipe is. I just took the word of the salesman when he said we have microbore. (I know!) However, I'm pretty sure he was looking at a radiator with copper pipes when he said that. (They have just been painted white). 

The correlation between a max 1kW radiator and microbore also has me a little worried! 

Thank you for your comments - it has motivated me to fire up Heat Punk!

Reed_Richards

Microbore pipes should be obvious to visual inspection.  Normal 15 mm pipes are a bit wider than your finger whilst microbore pipes are narrower.  They are only used for heating; I always think they look weird, more like a wire than a pipe.

Reed_Richards

The choice of outside temperature (-3 in your case) is not arbitrary but should be a temperature that is exceeded 99.6% of the time.  It should be calculated using data from your nearest weather station.  If you feel that it's often colder than that outside then you should query the choice of -3.  You might be able to do the calculation yourself, although I myself have never got my head around degree days.

70sbudgie

Heat Punk says that the outside design temperature for my postcode is -3.8°C. Given that the HP in the quote (Ecodan) gives similar numbers in Heat Punk, I suspect that they've just rounded the design temp up in the explanation.

I haven't managed to get emitters / heat loss calculation in Heat Punk to match the quote yet, but I suspect that is input error atm (ie me). 

Heat Punk has flagged something interesting about the noise assessment though - at 2m from the boundary fence, it is 43dB. So exactly where we put the HP is going to be important and it may have to be further along the wall than planned. This is relatively insignificant, to a point. So I'll have to actually measure it, carefully today. 

shinytop

Ecodan user here, or at least I was until I moved house last week.  They are the Ford Mondeo of heat pumps.  A solid, reliable workhorse. The same technology that powers millions of Mitsubishi ACs all over the world.  Mine worked flawlessly in the 3 years I had it and I expect it to keep going for many years to come.  I would/will have another.

My system cost about £16.5k (paid for by RHI) but that was for a complete system with 14 rads as we had no central heating previously. And it was a 14kW Ecodan.          

TroubledTarts

shinytop said:

Ecodan user here, or at least I was until I moved house last week.  They are the Ford Mondeo of heat pumps.  A solid, reliable workhorse. The same technology that powers millions of Mitsubishi ACs all over the world.  Mine worked flawlessly in the 3 years I had it and I expect it to keep going for many years to come.  I would/will have another.

My system cost about £16.5k (paid for by RHI) but that was for a complete system with 14 rads as we had no central heating previously. And it was a 14kW Ecodan.          

Surely being a Mitsubishi they are the Toyota or Honda of heat pump? 

shinytop

TroubledTarts said:

shinytop said:

Ecodan user here, or at least I was until I moved house last week.  They are the Ford Mondeo of heat pumps.  A solid, reliable workhorse. The same technology that powers millions of Mitsubishi ACs all over the world.  Mine worked flawlessly in the 3 years I had it and I expect it to keep going for many years to come.  I would/will have another.

My system cost about £16.5k (paid for by RHI) but that was for a complete system with 14 rads as we had no central heating previously. And it was a 14kW Ecodan.          

Surely being a Mitsubishi they are the Toyota or Honda of heat pump? 

OK then a Toyota Prius 

70sbudgie

I have been having further conversations with the company that provided me with the quote above. Based on my Heat Punk research and my subsequent questions to the installer, the quote now replaces more radiators and the design flow temperature has come down (albeit by only 2° to 45°C).

As part of the discussion, I was told verbally that the heat loss of my house has been calculated as 8.4kW. I asked if that meant I could install the smaller Ecodan unit. (8.5kW). The response in writing was "I would still be recommending the 11.2 kW system, I’m of the opinion that this is the best and most effective for your property." 

How hard should I push for the smaller unit? I am conscious of the discussions about oversizing, but at the same time, I don't want to install a HP that is too small.

NedS

FreeBear said:

70sbudgie said:

It has occurred to me that I might be able to make more of the quote I have had. For example by taking up the offer to change up to 10 radiators. Would this allow me to run the HP at a lower temperature (and therefore more efficient) or would my microbore pipework limit that regardless of the size of the emitter?

There is a limit to how much water can be pumped through a pipe. This restricts the volume of heat that can be delivered to a radiator. With a gas boiler running with a flow temperature of 70°C, 15mm will deliver ~6kW, whilst 10mm is restricted to ~2.5kW (with a ∆T20°C across the radiator). As flow temperatures drop, so does the ∆T, possibly as low as 5°C, so your 10mm pipe is only good for 1.15kW. 8mm pipe is even worse at just 750W.

If you can not increase the size of the pipe, you either need to increase the flow temperature (and the ∆T) or the flow rate. Increasing flow rate needs a more powerful pump, increases wear, and increases the amount of noise you'll hear. But... even with 8mm pipe running with a low flow temperature & ∆T, a 750W radiator is still going to be quite big. The T21 600x1000mm radiators that I have here are rated at ~1300W with a 70°C flow temperature. Drop to 40°C, and they only output 400W each - Well within the limits of 8mm copper microbore pipe.

For reference, when we ripped out and replaced our '10mm' microbore piping, I was surprised to measure an internal diameter of ~6mm as there were multiple layers to the plastic piping. Not sure if this is normal, but consider a 10mm copper pipe may have an internal diameter of ~9mm and it is the usable internal diameter that we are interested in when considering how much heat it can transfer, not the nominal outside diameter of the pipe in question (so a 10mm copper pipe could potentially carry 50% more heat than a 10mm microbore plastic pipe if internal dimensions are 9mm vs 6mm).

We kept the original microbore piping on one towel radiator in a bathroom where replacing would have required re-tiling, which is fine as it has a low heat output and we only require it to get warm to dry towels and are not dependant on it heating the room.