Most efficient way to run underfloor heating

Gerry1

matelodave said:

This heater seems to be on all the time - if you've use 28kwh in 14 days, thats about 2kwh a day or 80-100watts for the crankcase heater.(which seems quite good as mine appears to be around 120w = nearly 3kwh/day). The only way I've found to turn it off is to shut the whole heatpump off). I guess that the power consumed by the heater is calclated in the in SCOP but probably not in the raw COP and wont be taken into account in the heatmeter so you'll always use a bit more input energy than the heat output suggests.

Try doing your sums but discounting 2kwh/day for the crankcase heater

If the crankcase heater wastes up to 1000kWh or more annually, surely it must be worth installing a thermostat to control it?

matelodave said:

The rest gets wasted by my wife rinsing her hands and recyclable pots under the hot tap. She seems to be totally incapable of using cold.

Hope mrsmatelodave doesn't read this forum...

dllive

shinytop said:

You mentioned the ASHP is in the garage - is that correct?  I would have thought that would mean a cooler garage and a less efficient ASHP? 

The ASHP is sat on the exterior garage wall (obviously ), but the cylinder, pipework and Ecodan unit is in the garage. Would it usually be sited inside the house? Perhaps that explains the poor COPs. 

As Ive said earlier in this thread, the garage always seems warm. So either the pipework hasnt got enough lagging or the cylinder insulation isnt very good.

matelodave

I turned mine off on Sunday and left it for two days so i could judge how much hot water we got through and it's final temperature. We had plent of hot water on Monday and we both had showers

We've got a 200litre tank (1100mm x 550dia - including insulation), the temp sensor is 400mm from the top and the heating coil is between 520mm and 920mm from the top). It's not easy to judge exactly how much water got heated but I guess it's around 125-150litres (according to my calculation it requires about 1.74kwh to heat 150litres of water from 35-45 degrees)

The temp after 2 day was 35.2 degrees (and was still just about OK for a shower albeit a bit on the cool side) TBH we can just about get away with heating our water once every two days but the hotwater timer work on a 24 hour cycle 9although I could have 5 periods of heating if I wanted)

I turned the heatpump on at eight AM and let it run until the tanks had re-heated to 45 degrees. It took around one hour and ten minutes hour and consumed 1.46kwh of leccy. Which if you do the sums 1.74/1.46 implies a COP of about 1.2.

Here's the graph

matelodave

The fact that your tank and stuff shouldn't make much difference to the calculated or even actual COP because COP is the amount of heat produced by the heatpump compared with the amount of leccy that it consumes.

Even if all your heat gets lost in the garage it will not have any effect on the heat efficiency although it will on the efficiency of the heating system. It all depend on where the senors are located and what they are measuring. If your kwh meter is measuring the energy consumed by circulating pumps or any other stuff then it will distort the COP calculations.

If you look at all the reports (and even the RHI rules regarding monitoring) there are different options for measuring and measuring locations and all will give differnt results.

As I said, dont get too wound up about it. Exact COP calculations can only be done in a labratory under specified conditions.

Trying to do it at no 11 Aciacia Avenue with all the variations of time temperature,voltages and other thing that you can think of would require a lot of equipment, lots of sensors and quite a lot of computing power to integrate all the vaiables.

It's not always easy to understand all the info thats presented, how to interpret it and decide whether its really relevant.

Even a basic IHD connected to a smart meter seems to confuse more people than it should (that said, I wish I could get a bit more out of mine because what it does show has been dumbed down)

Reed_Richards

matelodave said:

A lot (if not all) air sourceheatpumps have a crankcase heater which stops the refrigerant from freezing or the oil separating out of the refrigerant.

I don't think mine does; I certainly cannot find any reference to it.  There is a buffer tank inside the house which is fitted with an immersion heater which my installer did not connect.  So if the outdoor unit wants heat it has to draw it from the buffer tank, I think.    

matelodave

Dunno what make your is - but look here, Ecodan have them (or some do) - https://www.navitron.org.uk/forum/index.php?topic=32030.0

I've never really seen all that much info about crankcase heaters but they have been mentioned in John Cantor's Heatpump blogs and I do know from all the installation specs and stuff that I got with mine (as well as the high standby consumption) that there's a crancase heater fitted.

I'm guessing that the manufacture's dont feel that a high standby consumption is a good selling feature and can be hidden t in the consumption/COP specs.

TBH it probably only becomes significant when the unit is running intermittently, like just heating water in the summer rather than when it's running virtually continuously during the heating season. In fact I've seen some specs where the COP for just heating hot water is lower than when it's providing space heating.

That's why the RHI is based on the SCOP rather than the COP as it's more representative of the whole season rather than a laboratory measurement made under ideal conditions.

dllive

This is slightly off-topic, but my energy company (Green Energy) has just gone bust! So Ill be migrating to another energy provider. (and hopefully my credit Ive built up!)

Because Im wholly on electricity (ie not gas) will my bills likely be the same? Or does the massive hike in gas prices also affect electricity users?

Thanks

matelodave

If the unit rate or standing charges increase then so will your bills.

Depending on how much wind there is some 30-50% of UK leccy is generated by gas fired power stations so the cost of leccy will be affected greatly by the price of gas.

See here http://www.gridwatch.templar.co.uk/ to see where its all coming from - the graphs show that the majority of it still does come from gas depite the odd days when wind output is greater

When the wind stops and the sun doesn't shine then the cost of generating leccy increases dramatically. We'll need a lot more wind turbines, but even then the wind isn't reliable so there will always be a requirement for some back up - they even had to fire up a coal fired power station last week because there was insufficient wind.

dllive

Hi @matelodave . Hope alls well.

Yesterday I noticed the pressure on the system was 0.5 bar. I increased it to 1 bar. ( I used this video to see how to do it  https://www.youtube.com/watch?v=QWLvg_VoPOk )

- Do you think low pressure could be the cause of my low COPs?
- Do you keep an eye on your pressure, and do you have to regularly/irregularly increase it?
- Should I increase it to 1.5 bar? (on the gauge there a red needle at the 1.5 bar mark, so I obviously dont want to go above that)



Thanks

matelodave

Not knowing exactly how you system is configured but generally the system pressure should be somewhere between 0.5-1.5bar. My pressure gauge is on the front of the hydrobox in the utility room (we've got a split system) and is obvious everytime we go in there so I dont actively keep an eye on it. It has drifted down to around 0.5 bar before I've topped it up back up to 1.5bar.

That said it's only done gone down that far a couple of times in the eleven years that we've had the system and the first time it was due to a weeping auto-vent valve, If it does it too often (or too quickly) it  indicates that the system is losing pressure somewhere. and should be investigated.

I had to de-pressurise my system last Christmas (actually on Boxing Day) due to a sticking flow switch - an easy fix that I sorted myself - I repressurised it to 1.5bar and it's still at 1.5 bar ten months later.

If yours is a monobloc system then be aware that your system probably has antifreeze in it, so make sure you dont dilute it to much (although a pint or so of water probably wont make much difference but it migh if you have to do it too often)

I can't see that a low pressure would have much effect on the COP and it's quite likely that if it dropped below a safe level then the machine would shut down.