You meet some damn stupid companies...

[ProDave]

I'm wiring a new house. It's going to be heated with an air source heat pump. I know I had to provide a feed to it, but nobody had yet given me the spec.  From past experience, I was expecting probably a C25 mcb (don't know why they still specify a type C when most heat pumps are inverter driven so don't have huge start up surges any more but that's an aside)

Yesterday, the house owner says "the heat pump guys are coming tomorrow"  Tough I say, it's the last week before Christmas and I'm still busy and still turning work away. but I agreed to go and at least have a look.  Bloody good job I did.

This time it's a split heat pump, not a monoblock. And they told me they will be installing a small CU for the heat pump and I just need to provide a 50A (50A FFS) feed to it.  No problem I will henley block off the tails for that (though I wish I had known and put the henleys in when I connected the CU)

"You can't do that"

"Why?"

"You have to provide rcd protection for our CU"

"Won't your CU have an rcd or rcbo's"

"No, you need to provide an rcd protected feed"

After initially telling them they are being silly and taking the urine, we agreed I will henley block off the tails to the new CU and I will change their main switch for an rcd. Stupid twats.

So I will be there tomorrow to do that, and I won't be letting the plumbers get in until I have done it, as looking at the layout of the room, access will be impossible once the HW tank is in.

 

 

[Sharpend]

Talking of Ashp's the lot I'm working with have took it upon the

selves to build an enclosure for the Ashp's thus rendering effectively useless, apparently the architect thought they were too ugly to be seen?? 

 

[ProDave]

THAT is a whole new subject. I was just moaning about the stupidity of supplying a CU without an rcd. What to they expect me do do, feed a rcd protected 50A submain of my CU?

When I questioned the 50A rating. "The heat pump is 25A, the controller is 13A, and the immersion heater is 13A, and they might all come on together".  I think he went to the Essex school of calculating max demand.

I don't know the make. All I saw today was the inside unit with it's cover off and no labels to say what make. I am sure I will find that out.

Now then, on the subject of heat pumps and the great RHI rip off.  The one I installed a few weeks back, was a Mistubishi ecodan monoblock ASHP with matching pre plumbed HW cylinder.  The customer paid £16K to have the "package" installed and claim the RHI.  I did some digging around and found you could buy the heat pump and it's pre plumbed cylinder for under £4K. They spent 4 man days on site connecting it and comissioning it. So even allowing for a decent rate for the plumber and sparky they sent, that's about £6K for the heat pump and labour to fit it.

So it would appear to me, he has paid a £10K premium, in order to have an MCS company install it in order to claim the RHI.  I bloody well hope (but somehow doubt) he will get more than £10K in RHI payments.

Ph and they didn't even bother to connect the "call for heat" from the UFH controller to the heat pump.

Another Great British con.



 

 

[ProDave]

I was in early to try and get it connected before the plumbers arrived. they didn't turn up until 9AM and I was finished by 9:30

Here's their CU. now modified to have an rcd instead of a main switch. There are three circuits, 40A for the heat pump, 16A for the controls and 16A for the immersion. Not that you would know as none were labelled.

The "mix and match" police will be along to fail this as you can see I have fitted a CED rcd into a Hager board. It was the only one that I had that fitted. (I did have a Hager rcd but only rated at 40A)  The CED one has the left terminal marked as N so I had to swap it around (main switch was originally on the right)

All their cables exit the bottom through a round hole they drilled and guess what, no grommet (the pathetic bit of grommet strip supplied was on top of the CU) I should ask them for their EIC and see how they answer 7.5 on the schedule of inspections.



It's a Daikin split Air source heat pump.

I love the qwality trunking install.



I wonder if they will fit the corner and tee pieces later on?

 

[Lurch]

Is there anything in there bigger than a 2.5mm²?

 

[Sharpend]

I think you'll find the immersion is only a secondary back up or at least it is on the ones I'm doing. 

The Ashp will do both water and heating, and you can set the external temperature at which you would like the immersion to assist Ashp for water. However given the Ashp are very efficient in lower temps it is unlikely that the immersion would need to kick in. 

 

[ProDave]

A heat pump system normally only heats the HW tank to 45 degrees. Beyond that the COP falls off severely. So the immersion is there to heat the tank to 65 degrees usually once every 2 weeks as an anti legionella measure.

All their wiring is in flex. Normal high temp white 3 core flex for the immersion and CY flex for the HP. Yes it looks like 2.5mm on a B40.  As far as I can make out, the 3 core CY is feeding two circuits. Brown from a B15, Black from the B40 and grey (sleeved blue) as N. So if both circuits draw full load, what will be the current through the common 2.5mm neutral?



 

 

[Sharpend]

A heat pump system normally only heats the HW tank to 45 degrees. Beyond that the COP falls off severely. So the immersion is there to heat the tank to 65 degrees usually once every 2 weeks as an anti legionella measure.

Thats what I thought, however when I questioned the technical heads and also the commissioning engineer they both said that with 'their' system the immersion is not required to do this. The HW temp in the tank from Ashp can be set upto 60 degrees. 

 

[ProDave]

Thats what I thought, however when I questioned the technical heads and also the commissioning engineer they both said that with 'their' system the immersion is not required to do this. The HW temp in the tank from Ashp can be set upto 60 degrees.

It will do that, but the COP will barely be above 1, if indeed it is as high as 1. So it's usually more efficiant to heat the tank to 45 degrees with the HP, then turn the HP off and raise the temperature to 65 with the immersion.  Of course best efficiency might not be their No 1 priority.
 

 

[Sharpend]

Iirc they said the cop will be not be lower than about 2? 

 

[rapparee]

I think you'll find the immersion is only a secondary back up or at least it is on the ones I'm doing. 

The Ashp will do both water and heating, and you can set the external temperature at which you would like the immersion to assist Ashp for water. However given the Ashp are very efficient in lower temps it is unlikely that the immersion would need to kick in. 

Totally correct. 

Our air source heat pumps only become useless at -20*C.