@parmstar sorry to hear about your problems. What is your heat pump model number, the calculated heat loss of your home and the design flow temp?

I just want to get an idea if this is something we can solve on the forum or if you need to pursue a fight with your installer which as you've noted might be difficult. 

@oswiu attached a copy of the design document which was sent AFTER the install was done upon request - it’s a Mitsubishi ecodan 11kw

@parmstar so on the temperature front it's clear they just didn't design as you asked. Your actual heat losses could be over 10% higher than that with the temps you want, so that might explain the problems getting to the right temperature recently.

There's definitely more to look into though. The £750 of electricity you used, is that all from the heat pump or overall? If that's just the heat pump then that is shockingly poor efficiency, so bad that I almost can't believe it's that.

Do you have data for how the heat pump itself is doing? There's a service called Melcloud that you might have been given access to that should give you some charts and figures, or if not your controller might give you info about energy usage, heat energy delivered, on time etc.

Any idea what design temperature they went for? That’ll help us determine if the rads are the correct size for the rooms and will help us choose what size heat pump should have been installed.

@oswiu thanks for getting back to me. There is no way of monitoring energy usage for just the heat pump as they installed the wrong model of control unit - this is a separate issue that I have raised with them. The figure quoted is for total electric which is stoll

way way more than my standard bill

@hugh  the first column of the table is the design temp

@parmstar that’s the room temperature. I need to know what flow temperature they designed for. This is the temperature of the water that flows round the radiators and makes a massive difference to the cost and performance.

For example, an 11kW ecodan will deliver 11kW at -3, but only when heating water to 35 degrees. That’s fine for running UFH at a proper pipe spacing, but no good for retrofit onto existing radiators.

Ask it to deliver 55 degree water and it will struggle to deliver 7kW (probably)…

Tl;dr - your heat emitters are too small

@oswiu 6.56kW continuous house usage for 14 days straight, at the backstop rate…

3kW into the heat pump and a 3kW backup immersion running too?

Or the ecodan running at a cop of under 2 because it’s uplifting to 50 degrees when it’s -5 outside?

@hughf flow temp is 50 but I have upped that to the max - most of the rads have been upgraded to much larger ones

@hughf the immersion heater is connected to an iboost so isn’t linked with the melcloud 

also forgot to mention the ASHP is facing a fence and is probably recirculating cold air which isn’t helping

Posted by: @parmstar

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@hughf the immersion heater is connected to an iboost so isn’t linked with the melcloud 

also forgot to mention the ASHP is facing a fence and is probably recirculating cold air which isn’t helping

 

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Therein is the likely issue with the majority of your performance issues.  The siting is not ideal as the cold expelled air has insufficient space to escape.  The ASHP is therefore having to draw in it's own expelled cold air and working it's nuts off to reheat that air.  Not at all well situated and unlikely to work efficiently.

@morgan no other place to site it unfortunately - the installer never made me aware of any of this and claimed it would be fine as it’s within clearances. It’s also within 1m of the property boundary which is a no no!

Wow the positioning of that heat pump is shocking. It's barely got any room behind it, it has almost no room around it, it's well closer than 1m to the property boundary and it's made an ice rink!

OP you might have luck getting the installer to move it by proving they've installed it contrary to the instructions in the manual. If they're registered with Mitsubishi, then I imagine Mitsubishi won't be happy with them... You're better off with a very well lagged longer pipe run in my opinion.

On the flow temp, 50C is quite high and so not the most efficient, but it's not the worst. Make sure you have weather compensation set up for when it gets a bit warmer.