DPC heatbank heat loss

[Bodgit]

I installed a Pandora heatbank from DPC about 2 years ago. It's always worked well but I've always been concerned that it seems to leak a lot of heat, but I've never got round to actually measuring it until now (had 2 kids in the meantime that took all my time!)

The design code is CPC-150-ABBDA-AAJA-H (150 litre Pandora) At 10.30pm the temp was 78 deg.C. At 8.00 am the temp was 64 deg.C.

It was completely powered down overnight, so the loss can not be due to a dripping tap etc.

I work that out as 8.8KJ over 9.5 hours, so an average heat loss of about 250W, which seems very high!

I'm wondering if such a high loss could be due to the fittings etc. or if it's likely that the insulation is compromised.

I emailed DPC a week ago but haven't received a reply as yet.

Any advice gratefully received!

Thanks, Dave.

[Tim S]

Bodgit coughed up some electrons that declared:

How thick is the tank insulation? 25 or 50mm?

Do you have pipe lagging on everything, including the expansion pipe (if this isn't an integral unit).

250W doesn't seem too massive (think how warm an airing cupboard is with a regular tank in) but it might be possible to improve it in situ.

You can get some polystyrene or 25mm celotex (Wicks and B&Q sometimes sell cut off small panels) and using toothpicks or tape, make little boxes to contain the plate heat exchanger and pumps (pumps: do NOT enclose the motor body or control, just make a little half box to go round the back and up the sides of the impeller section only).

Some of that will probably make a gnat's breath of difference but the cumulative savings might knock 50-100W off your leakage.

If you made a U-value assumption for the foam around the tank, it would be possible to take a wild guesstimate calculation for the expected leakage based on surface area and inner and outer face temps.

Also, there's usually naff all insulation under the tank (insulation won't take the wieght) - is it bleeding heat through the floor?

Nothing to stop you adding a tank jacket (big one) to the outside, as long as you don't cover up the electrical bits.

Overall, as your leakage happened overnight, I suspect your 250W is mostly going out the tank wall and immediately adjacent pipes, but that's doesn't invalidate insulating the other bits as they'll bleed when it's in use).

Just some thoughts, not a definitative answer...

Tim

[RubberBiker]

I checked your figures (and came to the same answer), and that does seem a lot. Could there be a convection current through the feed and/ or expansion pipes so that the header tank acts as a heat leak?

[fred]

In article , Bodgit writes

My 205L cylinder (not heatbank) quotes a loss equivalent to around 132W so your 250W for a smaller cylinder does sound a bit high but I could see a lot going through the extra pipework associated with a heatbank.

Are all the pipes around the bank fully insulated? I have 19mm walled pipe insulation on mine. Cylinder insulation is a fairly basic 35mm.

I don't think it's a major convection loop though, you'd be losing heat a lot quicker than that.

[Swift Half]

Hi All,

Thanks for the replies - some useful information there.

There are 4 pipes connected to the heatbank: boiler flow & return; mains cold water in and DHW out. The whole thing is in an airing cupboard under the stairs on the ground floor. I'm not sure how thick the insulation is - it's all enclosed in a plastic casing so you can't actually see the insulation. The surface temperature doesn't feel much above ambient though. It's sat on a piece of 18mm plywood, on a solid concrete floor, so there may well be some losses there. I don't suppose there's much I can do about that though.

The boiler flow & return are insulated inside the cupboard (first 4 feet), but they go through the wall and behind some built-in cupboards in the bathroom, so they're uninsulated for the next 6 foot or so, then they're fully insulated in the boiler room. The F&E tank connects to the pipework in the boiler room, on the other side of a motorised valve, so I really doubt there's a convection current running - the pipes in the boiler room are pretty cool anyway.

The heatbank came with a small amount of insulation on some of the heat exchanger pipework, but there are a fair amounts of elbows & unions that are uninsulated. I might try Tim's suggestion of insulation using Celotex - I'll have some left over in the next couple of months. Thanks for the suggestion.

I'm actually using the airing cupboard to dry clothes with the aid of a small dehumidifier (I got the idea from this NG), so the leaking heat is not going entirely to waste!

Thanks again, Dave.