Heat Pumps and "Microbore" pipes

Keiron42

Would like to pick the collective brains about Heat Pumps and a 25+ year old central heating system that uses 10mm "microbore" pipes.  
I have 250m of this piping and 19 steel radiators in my wet system along with a 300L HW tank.  The system is in good condition, works perfectly and keeps my well insulated (as well insulated as I can make it) home comfortably warm.  I fitted an EvoHome "Smart" heating control system a few years ago which resulted in a 20-25% reduction in our oil use (included optimising the HW tank temperature as well).
I'm reluctant to switch to a Heat Pump because of the lower flow temperatures which would require replacing all the copper pipes and all the steel radiators.  That just feels wasteful to rip out perfectly good and replace with brand new when it all works.  It also means ripping up expensive flooring to access the underfloor pipes, breaking plasterboard walls, repairing and redecorating (all additional expenditure)  I'm also concerned that to heat my HW to 50ºC+ for Legionella control I would have to use the expensive electric immersion, defeating the point of a Heat Pump.

So my question to the "hive mind" is - are there any Heat Pumps that can efficiently produce a Flow temperature of 60ºC, that would slot straight into my existing plumbing, use my existing Smart heating controls and provide a full 300L of {biologically safe} HW?

I'm also interested in options.  Say what Heat Pump could slot directly into the plumbing and rads with a Flow temp of around 45ºC (slightly longer heating up time but my Smart heating will learn to adjust to that) if I use a different option to provide HW? Or is there a system that would give "on demand" HW thereby removing the problem of having to heat the tank to kill Legionella bacteria.

Many thanks to all for the ideas and advice

Rodders53

How old is the Kerosene boiler, storage tank et al??

I will only look at HP replacement if/when the above are needing replacement. 
Then it'd be time to consider solar panels (which with diverter would electrically heat the HW tank to kill bugs) installed on the roof. 

With a COP of 3 and electric at 25 p a unit,  a HP will be a bit over 8.33 p per kWh of heat in,  
Kerosene for my last fill was 8.7 p per kWh (90% boiler efficiency) but electric was 30p a unit then... and Kerosene is currently below my last purchase price by some 13-14 pence per litre which will shave over 1 p off the per kWh price.

Small bore heating:  The only way to know if the low 45 C water flow could work is to do the full room heat loss calcs and do the numbers for the radiator sizes at the current vs proposed flow temps.  This is a scientific/engineering problem for you to work out.  Not a wet thumb in the air issue.

HP installers will need to do those calcs and recommend solutions.

If the small bore is long runs of it then the typical issue is water noise and wear to get the necessary flow rate (higher pump speed) to transfer the energy.  If the main feeds are large bore 22 mm pipes and manifolds feed local radiators in relatively short lengths, it may work better?

I think the modern wet ASHPs can reach high temps 55-60 C without using a 1:1 heater in them (like the older wet  ASHP had that gained them a bad reputation) and some can control the CH temp and HW temps differently by timers.  Plenty of places to Google such info.

Anyway that's my 2d worth on the subject.

MultiFuelBurner

A cop of 3 is very old school and underated these days. Expect a well setup system to obtain a cop of 4 and if you are an enthusiast a cop  between 4 and 5.

Again consider electricity prices, with a smart meter, of 18p kWh for electricity on the new tracker rates and if you can load.shufr a little 11-15p kWh for Agile and.thats before adding anything fancy like solar or batteries.

A heat loss survey and proper design paid for by heat geeks or a free one from Octopus is your best option imo. They will size a heat pump and replacement radiators and let you know what is possible. Thinking about it I think Octopus may not help out for microbore at this stage so to get the best professional advice heat geeks could be your best route to discuss your options. 

Netexporter

I think a "halfway house" solution might be workable. Keep the pipework but replace the radiators with double/triple panels ones of the same width, to achieve the correct heat output at a lower flow temperature, of say 45 degrees. You'd be best advised to get rid of TRVs, if fitted, to create an open loop system controlled by weather compensation.

This chap's experience may help/encourage you:

Microbore Heat Pump in Winter. How does microbore heat Pump perform on a cold winters day? (youtube.com)

Reed_Richards

Keiron42 said:

are there any Heat Pumps that can efficiently produce a Flow temperature of 60ºC, that would slot straight into my existing plumbing, use my existing Smart heating controls 

It depend what you mean by "efficiently".  Yes there are heat pumps that can produce water at 60ºC but they will be more efficient if you set them to 50ºC and even more efficient set to 40ºC.  If you try to achieve a drop-in replacement for an existing boiler you will save on installation cost but lose on running costs so it may be a false economy

Keiron42 said:

I'm also concerned that to heat my HW to 50ºC+ for Legionella control I would have to use the expensive electric immersion, defeating the point of a Heat Pump.

This really isn't the issue you think.  You heat the water to 50ºC with your heat pump every day.  Once a week you use the immersion heater to heat from 50ºC to 60ºC and hold it there for an hour, say, which is more than adequate to prevent Legionella.  That's really not defeating the point nor the economy of the heat pump.

 Keiron42 said:

Would like to pick the collective brains about Heat Pumps and a 25+ year old central heating system that uses 10mm "microbore" pipes.

Heat pumps usually use higher flow rates than boilers.  Achieving suitable high flow rates could be a problem with small bore pipes that have had 25 years to clog up.  That's why heat pump installers tend to fight shy of them.  

QrizB

MultiFuelBurner said:

A cop of 3 is very old school and underated these days. Expect a well setup system to obtain a cop of 4 and if you are an enthusiast a cop  between 4 and 5.

But not if you want:

Keiron42 said:

... Heat Pumps that can efficiently produce a Flow temperature of 60ºC

You can have a good COP or a high temperature.

MultiFuelBurner

QrizB said:

MultiFuelBurner said:

A cop of 3 is very old school and underated these days. Expect a well setup system to obtain a cop of 4 and if you are an enthusiast a cop  between 4 and 5.

But not if you want:

Keiron42 said:

... Heat Pumps that can efficiently produce a Flow temperature of 60ºC

You can have a good COP or a high temperature.

I did caveat everything with get a proper survey done from a qualified professional to advise what is possible for their particular property.

I do dislike these out of context quotes that don't take the reply as a whole. 

I was going to ignore it but thought it was poor quoting I might even say Daily Mail esque 🤣🤣

QrizB reporting for the Daily Mail (joking btw)

Reed_Richards

QrizB said:

You can have a good COP or a high temperature.

I'm afraid this is the inconvenient truth about heat pumps, not Daily Mail style reporting.  Any condensing boiler will perform more efficiently if run with lower return water temperatures but with heat pumps it's the leaving water temperature that matters and the drop-off in efficiency as you make that water temperature higher is much greater than with a condensing boiler.


   

FreeBear

Reed_Richards said:

Keiron42 said:

I'm also concerned that to heat my HW to 50ºC+ for Legionella control I would have to use the expensive electric immersion, defeating the point of a Heat Pump.

This really isn't the issue you think.  You heat the water to 50ºC with your heat pump every day.  Once a week you use the immersion heater to heat from 50ºC to 60ºC and hold it there for an hour, say, which is more than adequate to prevent Legionella.  That's really not defeating the point nor the economy of the heat pump.

Heat pumps are usually installed alongside an unvented DHW cylinder. So the only source of legionella is from the incoming mains supplied cold water - This water will have been treated, so the risk is extremely low. If you are reliant on a borehole or a stream/lake for your water, the risk of contamination is higher.

That said, with just 200-400 cases reported annually in the UK (approximately half contracted overseas), your chances of being infected is very, very low. There are much bigger risks in a domestic setting than legionella to worry about.

BellaBlondykeTheThird

Ah the great Legionella debate.

For what it is worth ASHP set to 52oC this time of year and stays there for two hours. It all gets used up which is the best way and refilled with treated cold water then heated again to 52oC for two hours. Rinse and repeat.

In the summer we only heat to 45oC

BellaBlondykeTheThird

Keiron42 said:

Would like to pick the collective brains about Heat Pumps and a 25+ year old central heating system that uses 10mm "microbore" pipes.  
I have 250m of this piping and 19 steel radiators in my wet system along with a 300L HW tank.  The system is in good condition, works perfectly and keeps my well insulated (as well insulated as I can make it) home comfortably warm.  I fitted an EvoHome "Smart" heating control system a few years ago which resulted in a 20-25% reduction in our oil use (included optimising the HW tank temperature as well).
I'm reluctant to switch to a Heat Pump because of the lower flow temperatures which would require replacing all the copper pipes and all the steel radiators.  That just feels wasteful to rip out perfectly good and replace with brand new when it all works.  It also means ripping up expensive flooring to access the underfloor pipes, breaking plasterboard walls, repairing and redecorating (all additional expenditure)  I'm also concerned that to heat my HW to 50ºC+ for Legionella control I would have to use the expensive electric immersion, defeating the point of a Heat Pump.

So my question to the "hive mind" is - are there any Heat Pumps that can efficiently produce a Flow temperature of 60ºC, that would slot straight into my existing plumbing, use my existing Smart heating controls and provide a full 300L of {biologically safe} HW?

I'm also interested in options.  Say what Heat Pump could slot directly into the plumbing and rads with a Flow temp of around 45ºC (slightly longer heating up time but my Smart heating will learn to adjust to that) if I use a different option to provide HW? Or is there a system that would give "on demand" HW thereby removing the problem of having to heat the tank to kill Legionella bacteria.

Many thanks to all for the ideas and advice

Heat geeks recommendation here even paying £500 for the survey. Our neighbour got a fantastic system installed outstripping the economy of ours by a third. A well designed setup system is what you want and microbore will not give that to you.