Heat Pumps and 10mm Microbore Piping

[Plumb]

Its not a fact. You are kind of correct though. Its the surface area that is important not the cross sectional area. Thats why radiators are so effective

So a narrow pipe has a greater surface are (relatively) than a big pipe.

You are arguing with a scientist and not a plumber

Sorry not arguing just a different approach a larger cross sectional area equals a greater circumference so the same thing as bigger or smaller pipes splitting hairs come to mind

 

[Plumb]

And doesn't hot water carry units of heat. The hotter the water the more units of heat. The greater the volume (flow) the greater the units of heat entering the radiator.

Of course hot water carries units of heat but flow rate does not increase the units of heat you are sending you are talking about the flow rate through the circuit to and flow to the radiator .

 

[gpat]

Of course hot water carries units of heat but flow rate does not increase the units of heat you are sending you are talking about the flow rate through the circuit to and flow to the radiator .

Yes I am talking about the flow to the radiator. Each litre of water flowing to the radiator contains a given quantity of heat. The quantity is proportional to the temperature.

So if a room requires a certain amount of heat you have numerous choices, the extremes being

1) Massive amounts of water with a small amount of heat or
2) Small amounts of water with massive amounts of heat

With ASHP you have limited heat in the water going to the radiators so you must cater for this by having, not only bigger radiators but also higher flows of water to transport that lower heat.

It called balancing the equation.

Not splitting hairs at all. Just getting the understanding of the physical science

 

[mikebeaches]

So we have very recently been quoted circa £17.5k to replace our oil boiler with an air source heat pump system.

We live in a mid-80s detached four bed split-level bungalow. Walls and roof fully insulated, but suspended floor that isn't, and with lots of airbricks too.

Unfortunately, I'm far from persuaded at the moment.

The oil boiler is old (21 years) but regularly serviced by an excellent technician that lives in the village. It still works perfectly and he assures us it's got years of life left...

 

[acropolis22]

So we have very recently been quoted circa £17.5k to replace our oil boiler with an air source heat pump system.

We live in a mid-80s detached four bed split-level bungalow. Walls and roof fully insulated, but suspended floor that isn't, and with lots of airbricks too.

Unfortunately, I'm far from persuaded at the moment.

The oil boiler is old (21 years) but regularly serviced by an excellent technician that lives in the village. It still works perfectly and he assures us it's got years of life left...

What did the £17.5k include out of interest? All new rads presumably? Seems high though.

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[gpat]

So we have very recently been quoted circa £17.5k to replace our oil boiler with an air source heat pump system.

We live in a mid-80s detached four bed split-level bungalow. Walls and roof fully insulated, but suspended floor that isn't, and with lots of airbricks too.

Unfortunately, I'm far from persuaded at the moment.

The oil boiler is old (21 years) but regularly serviced by an excellent technician that lives in the village. It still works perfectly and he assures us it's got years of life left...

I wouldn't even be thinking about it. Fair enough if your boiler breaks but there is no benefit at all for you to change at the moment.

 

[Plumb]

Yes I am talking about the flow to the radiator. Each litre of water flowing to the radiator contains a given quantity of heat. The quantity is proportional to the temperature.

So if a room requires a certain amount of heat you have numerous choices, the extremes being

1) Massive amounts of water with a small amount of heat or
2) Small amounts of water with massive amounts of heat

With ASHP you have limited heat in the water going to the radiators so you must cater for this by having, not only bigger radiators but also higher flows of water to transport that lower heat.

It called balancing the equation.

Not splitting hairs at all. Just getting the understanding of the physical science

Sorry I am going to have to have a lie down I'll be back !

 

[Plumb]

So we have very recently been quoted circa £17.5k to replace our oil boiler with an air source heat pump system.

We live in a mid-80s detached four bed split-level bungalow. Walls and roof fully insulated, but suspended floor that isn't, and with lots of airbricks too.

Unfortunately, I'm far from persuaded at the moment.

The oil boiler is old (21 years) but regularly serviced by an excellent technician that lives in the village. It still works perfectly and he assures us it's got years of life left...

Unless it's absolutely necessary to change don't bother you woul have to live to be a thousand to get your money back , and then it's doubtful

 

[gpat]

Sorry I am going to have to have a lie down I'll be back !

If you really want me to I will work it out mathematically.

How much energy is lost when 1 kg of water cools from 100°C to 25°C?

ΔEtQ=m c Δθ

ΔEtQ=1×4,200×(100−25)

ΔEtQ=1×4,200×75

ΔEtQ=315,000 J

For every degree you are less than 100C you get less heat into the room. So you need to increase the number of kilograms accordingly. That means more flow.

 

[Spriddler]

Nothing scientific, just anecdotal, but 5 years ago my son moved to a new detached house with air source heating. The underfloor heating is O.K. but he has to use the electric immersion heater to achieve a water temperature suitable for showers.
He has had the builder back twice who says (unsurprisingly) that there's nothing wrong with the installation.

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[mikebeaches]

What did the £17.5k include out of interest? All new rads presumably? Seems high though.

9 new radiators, which is almost two thirds of them from memory.

 

[acropolis22]

9 new radiators, which is almost two thirds of them from memory.

As others have said, I can't see why you would change if the old system is still going OK. It's always going to be a struggle in a retrofit situation too.

 

[gus-lopez]

Sorry that’s not true a pipe with a larger cross sectional area will dissipate more heat than a smaller cross sectional pipe ! That’s a fact .

I would expect all & any type of pipe run to be insulated.
If I run water at 85º through 25mm pipe with short 15mm tails to each rad I would expect heat above 65º within a short time at each rad. It won't happen with micro bore due to the sheer lack of quantity of flow.

The oil boiler is old (21 years) but regularly serviced by an excellent technician that lives in the village. It still works perfectly and he assures us it's got years of life left...

Don't even think about it.

but suspended floor that isn't, and with lots of airbricks too.

My mate had super insulation in walls & roof on a rental he had that he now lives in . People complaining of draughts. traced to the only possible option being the floor. He was fortunate in have a 20" crawl space below the floor boards as he had to get the underside of the floors between the joists insultated by having it suspended hung . Nightmare of a job. Worked though

 

[gpat]

. but he has to use the electric immersion heater to achieve a water temperature suitable for showers.

The water should be easily hot enough for a shower, Something wrong there. Ideal temperature for a shower is around 40C and heat pumps produces water at around 56C.

 

[mikebeaches]

As others have said, I can't see why you would change if the old system is still going OK. It's always going to be a struggle in a retrofit situation too.

I don't think we are going to change.

However, I still clearly recall when the previous oil boiler pegged out... sods law, in the middle of January arctic conditions!

It took a while to get it replaced too. Brrr. And now we're getting a bit long in the tooth.

So considering options - which to be honest are somewhat limited.

But I agree with the consensus on here - an air source heat pump is not for us, at the moment. And I'd even paid quite a bit for a comprehensive heat loss survey!

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[Plumb]

If you really want me to I will work it out mathematically.

How much energy is lost when 1 kg of water cools from 100°C to 25°C?

ΔEtQ=m c Δθ

ΔEtQ=1×4,200×(100−25)

ΔEtQ=1×4,200×75

ΔEtQ=315,000 J

For every degree you are less than 100C you get less heat into the room. So you need to increase the number of kilograms accordingly. That means more flow.

 

[gpat]

I don't think we are going to change.

However, I still clearly recall when the previous oil boiler pegged out... sods law, in the middle of January arctic conditions!

It took a while to get it replaced too. Brrr. And now we're getting a bit long in the tooth.

So considering options - which to be honest are somewhat limited.

But I agree with the consensus on here - an air source heat pump is not for us, at the moment. And I'd even paid quite a bit for a comprehensive heat loss survey!

Yes. If you are worried about the gas boiler conking out. Get another now. They are about £1500 fitted. That's less than 1 tenth of the price of a ASHP and you will have peace of mind for years. Probably cheaper to run as well. You won;t have to worry if your house will be warm enough either

 

[Plumb]

If you really want me to I will work it out mathematically.

How much energy is lost when 1 kg of water cools from 100°C to 25°C?

ΔEtQ=m c Δθ

ΔEtQ=1×4,200×(100−25)

ΔEtQ=1×4,200×75

ΔEtQ=315,000 J

For every degree you are less than 100C you get less heat into the room. So you need to increase the number of kilograms accordingly. That means more flow.

Yes sorry nice one found exact same formula on bbc bitesize website

 

[Ejaydee]

So we have very recently been quoted circa £17.5k to replace our oil boiler with an air source heat pump system.

Ouch, that is well over double of what it cost me to fit my Mitsubishi Ecodan PUHZ-W85VHA-BS unit a couple of years ago. However, I did already have Thermoskirt (aluminium skirting radiators) fitted in most rooms already, so it was effectively a replacement ASHP for a cheap clone ASHP that had been installed 8 years previously.

 

[mikebeaches]

Yes. If you are worried about the gas boiler conking out. Get another now. They are about £1500 fitted. That's less than 1 tenth of the price of a ASHP and you will have peace of mind for years. Probably cheaper to run as well. You won;t have to worry if your house will be warm enough either

Small problem - our boiler is oil-fired, no gas in the house.

But it does now run down the road outside, so I need to explore the cost of getting the gas to the house - which will require digging up the tarmac drive.

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[MisterB]

I assume it will be that price (£17.5k) because they will take a massive profit from the govt subsidy, yes you will get your grant but they will fit, fleece and fly if they're anything like the solar panel installers that suddenly surfaced during the big last govt grant giveaway..... Only to disappear over the horizon at sunset, probably riding horses ..

 

[acropolis22]

Small problem - our boiler is oil-fired, no gas in the house.

But it does now run down the road outside, so I need to explore the cost of getting the gas to the house - which will require digging up the tarmac drive.

Anyone checked on relative costs by fuel type since the price of gas went through the roof? Has oil gone up too?

 

[mikebeaches]

Anyone checked on relative costs by fuel type since the price of gas went through the roof? Has oil gone up too?

Price changes here, from Boilerjuice:

Home Heating Oil Prices & Charts UK | BoilerJuice

View today's average UK heating oil price and work out when the best time to buy is with our daily price chart.

www.boilerjuice.com

So April/May 2020 price was down to around 20p per litre, and now circa 65p a litre!

 

[Bolti]

The price of crude oil is at a 7 year high

 

[gpat]

Small problem - our boiler is oil-fired, no gas in the house.

But it does now run down the road outside, so I need to explore the cost of getting the gas to the house - which will require digging up the tarmac drive.

The same applies for an oil boiler. We have one too. Still better and cheaper than ASHP. Just up the estimate to nearer £3500 to £4,000 for a new one

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[acropolis22]

The price of crude oil is at a 7 year high

Everything is going up. We could turn this into a cost of living thread?

 

[gpat]

Yes sorry nice one found exact same formula on bbc bitesize website

Its a well known formula in the process industry

 

[SpeedyDux]

Small problem - our boiler is oil-fired, no gas in the house.

But it does now run down the road outside, so I need to explore the cost of getting the gas to the house - which will require digging up the tarmac drive.

A question to consider is whether in the medium to long term it will be better to stick with oil.

The direction of energy pricing policy is to raise the domestic gas tariff (KW/h equivalent) to whatever the electricity tariff will be in a few years' time when most electricity comes from renewables. In order to speed up Net Zero, the latest Climate Change Committee Report has given advice to the government to that effect. The objective will be to phase out gas for domestic heating and replace it with heat pumps or hydrogen by 2050. As long as the cost to the consumer of gas is significantly less than the cost of eletricity or hydrogen that change is unlikely to happen fast enough through natural progression.

I have seen nothing that says the price of heating oil will be artificially increased to match electricity or hydrogen. A relatively small percentage of homes rely on oil for heating. I could be wrong, but if heating oil remains tied to the crude oil price it might well turn out much cheaper than gas in the long run. The oil price should continue to follow the market instead of Green policies.

 

[Stroppy Bird]

I've looked into changing our 18yr old oil combi boiler several times over the last few years (mainly cos I hate where it is).

Last year I had a company round to quote for ASHP. It came in at £12k which included a hot water cylinder and 7 new radiators.

BUT.... when I questioned them about the microbore supplying my current rads they said that they could use it if it was 10mm but not 8mm. A friend of the family (not local) also works for a company fitting ASHP said they would always replace microbore with 15mm. I don't particularly want retrofit pipe work on show.

Also, I did the size calculations for replacing the living room radiator. Due to the room layout and it being under a window, there isn't a radiator that can throw out enough heat at the lower temperatures that would fit in the current position. So back to retro-fit exposed pipework that I don't really want and a second radiator fitting somewhere in the living room - or UFH, which would be nice, but again, even more expense.

And just to throw in the mix - location for a hot water cylinder - the company who quoted suggested the loft. The problem here is that our loft is with modern trusses and wasn't designed for such load bearing - it would probably be ok if the weight was spread correctly (I think the old 2011 NHBC regs did a nice diagram). But this would incur extra cost in making it suitable and getting signed off for building regs. And again - more exposed (or boxed in) retrofit pipework would be needed to get the water to and from the loft.

The company that did the quote also estimated how much electricity the ASHP would use per year. If electric remained at about 20p per kWh then oil would need to be 75p per litre based on my current usage for the ASHP to be as cheap to run.

So all in all, I have decided to stick with oil for the time being.

Hopefully HVO will become available at a reasonable price in the future so that I can use the same boiler (though to be fair, I'll probably change to an external combi) and tank and be a bit greener too. It's currently being trialled in a few areas as a drop in replacement for heating oil (Cornwall, mainly I think), but doesn't seem to be overly well promoted as a possible greener alternative for off gas grid houses.

For a balanced view, two new builds in our village were built with ASHP, and both seem to cope with it absolutely fine, though they were designed with UFH and a heat recovery system.

We also looked at a retrofit ASHP in our village. It was lovely and warm when we went in - then we saw the log burner roaring away in the central 'drawing room' with all the downstairs doors open to let the heat circulate - hmm .

 

[Odd-no-more]

I have just received the quote for my air to air heat pump, just under £1,300 plus VAT. I have not as yet worked out the payback period but if gas does double in price it should be a reasonable time. I have a choice of 1 unit or 2 units but there's not a great saving getting 2 so I will just get one for now. I have experience of these in an office situation but I'm not sure how noisy it will be in a home environment. If it all goes wrong at least I will gain air-con in our south facing living room.

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