Much appreciated.

Regards

Bob

An LCT Application is for all sites where a heat-pump or EV charger is to be connected to an existing supply.

To see an example of where I believe the assessment has 'gone wrong' have a look at my comments on the topic about Twin 10kW ASHPs with volumisers.

Thanks

Bob

Yes, you can install a heat-pump on a DIY basis.

The legal requirements you need to fulfil are:

• Apply to your DNO using their online process for Low Carbon Technology (LCT)
• Get the mains electrical connections installed, or approved by, a qualified electrician who will supply you with a Building Regs Part-P certificate
• Apply to a Building Control organisation, such as your Local Planning Authority, to address Part-L and any other issues such as noise complience

Let us know if you want any of the above explained more fully.

Am I allowed to self install a heat pump in the UK?

It would be the only one on the property.

It would be at least 1m from the boundary.

The size of the machine would be less than 0.6m3.

I am not MCS registered.

Thanks

Bob

It's mainly sold in Australia & NZ where they want cooling as well as heating.

Mitsubishi heat pumps works great in low temperatures. Requires minimal maintenance. Here in Victoria, they are offered under government rebate program.  

You have a plate heat exchanger for system separation don't you? 

Yes, I do. I also have glycol in the primary circuit, and use a specific heat capacity of 4.05 for that (I noticed you use 4.2 ie pure water). The secondary circuit has quite a large volume, I haven't formally worked it out, but there is one huge K3 in the kitchen (15L?) plus several medium sized K3s and a few smaller ones, Perhaps (guessing here a bit) 100L in all just in the rads.

With a plateHex i get 7.7kg ice, no hex 4kg.

Either way, that is a lot of ice. Credibility/sanity check?

I've also worked out your primary system volume, 20L.  That's small.  You have a plate heat exchanger for system separation don't you?  Once the LWT starts to drop the plate exchanger will start to pull energy from your radiator system - you did mention this in one of your posts.  But you will only get good heat transfer over the plate exchanger if there's a large DT between hot and cold.  I think that explains the rapid increase i LWT after the defrost, from 27C to 38C in one minute, then the slow recovery in LWT because it's transfering heat into the radiators.

You can change Base!N14 0/1 to specify 1=platehex, 0=no plate hex.

With a plateHex i get 7.7kg ice, no hex 4kg.  I'm going to need to think a bit more about how to model this.

Bob

The data show's your room temperature is 25C and never changes, is that correct?

No! I mentioned this in the post that has the download ("ignore them, along with some of the never change columns eg room_temp which is Midea's idea of room temp!". Room temp is MD02_temp (an independent sensor).

I've worked through the data and estimate there's about 3kg of ice on the ASHP fins.  Ive attached a spreadsheet with the analysis, hopefully it works, I'm using OpenOffice.

Very interesting. If base load (8.4kW) is the total heat loss as derived from this data you have, it is as expected a bit on the low side because at these OATs my heat pump can't quite cope, that's why the room temp is around 17.7, rather than 19 degrees (my preferred room temp) or 21 degrees MCS/design room temp. My empirical heat loss (ie from observations rather than using a whatiffery calculator) is probably around 9kW at -4 degrees. Note the day the data you have been using comes from the day when it was very cold, and for the first time I really did crank up the heat pump to max, ie it has never worked harder (but was still within its operating range, for obvious reasons). 

Going back to your original question ("how much energy ASHP uses during a defrost cycle"), I think my first observation has to be that all the energy comes from the hot water in the pipework/rads, none from the rooms (which makes sense, the MD02_temp doesn't from during the defrost) or the heat pump itself (note also amps in drop very low during the defrost). The amount then, surely, is the amount that flows back into the heat pump from the rads and pipework, ie the negative energy out flows?

The reason defrosts matter so much is not just what happens during the defrost, when the heat pump is not producing any new heat for the house, it is also because of the long recovery period, with up to a half or more of the cycle running with an actual LWT below the set LWT, sometimes well below. If I can borrow your chart from your spreadsheet: 

The set LWT during the period shown is 58 degrees, but the actual LWT only approaches that during the second half of the cycle.