Heat Pump Questions

Telegraph_Sam

Verdigris said:

Telegraph_Sam said:

These are what-if scenarios which require accurate crystal ball technology.  I am trying to gauge what the advantages of a heat pump would be as things stand at present or in the very near future.

So, do you not take future scenarios into account when, say, choosing what car to buy and what fuel option would be most cost-effective?

For future scenarios read guesswork. Taking these (there are more than one) into account is one thing, basing a major decision like replacement CH on one or other happening is dangerous. Hence  the motivation for investigating and weighing up the pros and cons in advance

I tend to agree with the views expressed in the last two posts if I have understood them correctly.

Reed_Richards

Replacing a gas boiler with another gas boiler is much cheaper and simpler than replacing a gas boiler with a heat pump. And at current prices for gas and electricity the running cost of a gas boiler are less than a heat pump.  But heat pumps are very green because on average you will get about 3 units of output heat for every one unit of input power.  That, I think, is greener than an electric car and lots of people have been persuaded to pay a hefty premium for one of those.    

Telegraph_Sam

I will take your "3 for 1" argument at face value, not understanding the physics. But if the costs of running a gas boiler are less than a heat pump then the break-even point from installing the latter is infinity (until the market changes) and the motivation has to be environmental rather than economic.

Gerry1

Reed_Richards said:That, I think, is greener than an electric car and lots of people have been persuaded to pay a hefty premium for one of those.    

However, once you've paid the hefty purchase surcharge there are some advantages with an electric car.  It'll be quiet, automatic, have good acceleration, and there are fewer moving parts that need servicing.  For the time being it'll be cheaper to run and drive in central London.

Unless you can't get gas, you're unlikely to find any advantages with a heat pump (other than being relatively green) that will justify the high capital costs.

Telegraph_Sam

That in essence is the advice I had been seeking when I first posed my question.

Different scenario: Large traditional countryside residential building in central Scotland built in the 1700's when heat conservation and insulation had never been dreamed of.  Limited improvements in the interim but very difficult to get anywhere near the standards of modern construction. Not serviced by the gas network, dependent on oil for central heating. Outside winter temperatures in Perthshire can be very low. In this oil versus heat pump scenario I have conjectured that it would not be worth considering / investigating the latter even though expenditure on oil is high.  Am I right? [a. subsidized, b. not subsidized]

Reed_Richards

I replaced an oil boiler with an ASHP.  I've had the ASHP for 49 weeks now and it looks as if the running costs will be similar to what I was paying for oil.  In the case of a large poorly-insulated building there might be an issue getting a heat pump with a large enough output capacity.  However you can buy hybrid boilers which combine an oil boiler with an ASHP; possibly an option worth looking at.

Gerry1

It seems the fuel costs for oil and heat pumps are comparable at the moment, so after a hefty capital outlay you'd be back where you started.

Oil servicing costs may be higher, and oil can leak or be stolen, but the only real benefit is likely to be just a nice warm glow from being green.

matelodave

Saving energy isn't quite the same as saving money.

For most people at the moment ,mains gas is still the cheapest way to heat your house bar non (unless you can get free duel) and will remain so  until the price of 1kwh of leccy comes down to less than three times the cost of  1kwh of gas or if the price of gas increases to counteract the imbalance.

The only advantage in changing a mains gas boiler for a heatpump is that it may save energy but it certainly wont save you money, especially with the current gas/leccy price differential. 

I will take your "3 for 1" argument at face value, not understanding the physics. But if the costs of running a gas boiler are less than a heat pump then the break-even point from installing the latter is infinity (until the market changes) and the motivation has to be environmental rather than economic.

The 3:1 ratio (or SCoP*) is certainly achievable in a properly specified, commissioned and operated system but it's an average over the whole year, it's likely to be nearer 2:1 or less when it's very cold and could get close to 4:1 in the "shoulder " months. If you look at the specifications for heatpumps you can see how the CoP *varies with flow temp and input temps. 

Without having sophisticated and calibrated test equipment I reckon my eleven year old heat pump achieves  an SCoP* somewhere between 2.5 and 3

* SCoP and CoP are different insofar as CoP is measured at a specific flow temp against a specific outside temperature, whereas SCoP is an an average calculation based on the system performance over a year taking into account seasonal variations in the outside or input temperatures against flow temperatures.

Lots of info on t'interweb if you are really interested

Telegraph_Sam

Yet another variant to consider! [how a hybrid boiler would stack up]

The oil boiler can provide the heat (at a cost), I was / am more concerned about what people say about maintaining the internal temperatures within certain limits for an ASHP to function efficiently. Added to which if there are no significant advantages in running costs then it would take an eternity to amortize the investment.

Edit: This refers to @Reed-Richards latest reply.
I fear that the finer points of SCoP and CoP are way beyond my pay grade and enough to scare anyone off heat pumps from the outset.

Telegraph_Sam

Ignorant