Posted by: @grahamf

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You need to be confident enough to deal with the concerns of well-meaning relatives and friends, who may warn you that you are making a terrible mistake!

The oil industry sponsored right wing press has, without a doubt, done a fabulous job of convincing people that heat pumps are rubbish, albeith that the industry itself has made a fair contribution to this endeavour.  

They tried the same with EVs but appear to have been much less successful and are now even beginning to sound positive about them.

I can resonate with many of your comments based on my own experience.  The outcome was successful and the installation in practice straightforward, but finding an installer to quote a sensible price for a system that would do the job proved quite challenging.  Ironucally I ended up with someone very local, but got there through a very roundabout route.

When you do get to test please post back about your experience.  I trust that you have read about how best to operate them.  This is pretty much the polar opposite of how we operate boilers in the UK so you need to forget almost everything you learned about that!  Given your physics degree I'm sure you not only have but also understand why!

Just to add my observations, exploring a heat pump for a 4 bed house:

1. I was surprised how rigid and inflexible suppliers are about hot water cylinder capacities, with an existing cylinder in an airing cupboard I thought the hot-water side of the installation would be problem free - old cylinder out, equal sized new heat pump cylinder in, what's the problem?

Actually it's a minefield because many installers rigidly follow the MCS set sizing formula, which can result in a much bigger cylinder than your existing one, which may not fit in the existing space, with installers proposing really inconvenient and poor solutions, like moving the cylinder into a bedroom (who wants a cylinder in a bedroom?), or into the garage (losing heat into an unheated space), or knocking through walls to expand the space (lots of mess and cost for a few extra 50L of hot water)

When you tell them you are happy with the existing cylinder size and would much prefer a smaller cylinder which fits into the existing available space, most can't offer anything (I assume because of MCS rules compliance for the BUS grant) and try to convince you why you now need a much larger cylinder.

2. Most installers only offer unvented cylinders (UVC), so where you have an existing vented cylinder with a cold water tank in the attic, even where this arrangement works fine, they will want to rip all of this out and converter to UVC. Despite UVC being more complex, expensive, requiring a drain pipe installing for the pressure relief and needing annual maintenance by a G3 plumber. 

@temperature_gradient As far as I am concerned you are pushing at an open door! I realise that the additional internal pipework may need to be increased to equate to the heat emission of a higher running temperature heat source (gas boiler fr’instance) but I think MCS requirements are more a rear covering exercise at the homeowner’s expense.

The above is the reason why I chose a Sunamp Thermino ePV210 heat battery system. We just did not have the space to accommodate a cylinder as fat or high as one with the capacity MCS specify for a 4 bedroom residence. The two of us existed quite happily with a 99 litre tank before and never ran short of hot water! Regards, Toodles.

@temperature_gradient I had two installers willing to work with our existing hot water tank, which isn't designed for a Heat Pump, though it is already pressurised.  I understand it won't be quite as efficient, but the added cost of heating the water, will probably take over a decade to offset the cost of a new tank, plus the waste of throwing away what is as of now a perfectly good, high quality tank.

Our install should be in the next month, so I'm hoping it all works as expected, but we have been running our gas boiler at 55C flow (dT 11) for heating and hot water for 3 years without issues, so I'm living in hope.

I hope you've opted for weather compensation controls from the start. Strongly recommended both for comfort and cost.

Depending on tariff choices there may be other tweaks.. but focus on WC first... our system has been in 5 years but wasted a lot of time, money with fixed controls for first 2 years

Posted by: @scalextrix

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@temperature_gradient I had two installers willing to work with our existing hot water tank, which isn't designed for a Heat Pump, though it is already pressurised.  I understand it won't be quite as efficient, but the added cost of heating the water, will probably take over a decade to offset the cost of a new tank, plus the waste of throwing away what is as of now a perfectly good, high quality tank

The business of throwing away perfectly good tanks really annoys me.  There is a perfectly good solution to a small coil even if you insist on max efficiency, namely to 'plate load' by fitting a plate heat exchanger and circulation pump around the tank. 

I found one installer who, even if you are replacing the tank, fits a coil-less tank and this arrangement.  Arguably it's a better technical solution anyway.

@tim441 thanks, and yes we are going WC for the central heating.

Unfortunately our boiler control only allows us to set a single fixed temperature for heating and hot water.  In winter we could heat the house at 50C flow, but to recharge the hot water in a reasonable time needs 55C flow.  Obviously to do these experiments required playing with boiler settings a few times a day and isn't sustainable for more than a few days in a row.

Honestly if we could have had WC on our existing boiler we would have gone that way, but it's 19 years old and I couldn't find anyone interested in fitting new controls.

We got lucky and hit gold with our installer. Rather than size radiators to a design temp, we came at it from the opposite direction of lets measure the wall space and fit the largest radiator we can accommodate, and then check it's output at least meets the design temp. Due to a combination of an over-estimated heat loss, and oversized radiators, we are now able to run with flow temps of 30-35C all year which significantly improves our operating efficiency compared to running 50C flow temps in the coldest depths of winter.

The two factors that most affect efficiency, and thus operating costs, are flow temperature and outside ambient temp, and they compound each other to destroy efficiency in winter, requiring higher flow temps just at the very time it is coldest outside. You can't control the outside temps in winter, but you can design to the lowest flow temps possible by fitting the largest emitters possible.

@scalextrix which make of heat pump. 

We have LG... which seems OK even though controls & data are not the finest...

On WC we heat central heating mostly around 35-40deg in a range 30-45

But it also heats the hot water very rapidly - we target 50deg at night on cheap tariff and top up at lower temps in the day. It heats in under 30 mins  even if heavily used.

@jamespa yes, I agree that there are a number of parallels with the reporting on EVs.  I am an enthusiastic EV owner and get frustrated by all the negative PR.  I use the Intelligent Octopus Go tariff, so the 7p per kWh will come in handy on cold nights.

We are well set up for the heat pump, thanks.  The hot water system is working well.  It is scheduled to run for 1 hour every night.  I have needed to top it up for nearly an hour in the evenings, but that is probably due to a hot water recirculation loop running through uninsulated pipes, which I plan to fix tomorrow.

We have beefed up the radiator capacity significantly, including some very chunky K3s.  My installer had a list of radiators to upgrade and I also had my own list.  We installed everything that was in either list.  We are running an open loop system with just one zone.  We have TRVs in the bedrooms and a lounge that gets hot in the sun.  I am starting all of them on maximum.  I have weather compensation curve set on a frugal level, which I will inch up as necessary.  The room thermostat is configured to reduce flow temperature, rather than turn off the system.    

All I need now is some bad weather to test it on!

@tim441 thanks for the advice.  The weather compensation is all set and ready to go.