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Hello Members, this is my first post and I'd like to say that I really appreciate Jeremy's Heat Loss Calculator, which took one day to complete (yesterday). The compact one-page format with 'what-if' ability is very, very useful. Thank you Jeremy.

These are my current considerations and I'd appreciate any comments and/or advice from members

Regards, Hugh


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Hi @kla456 and welcome to the madhouse :) 



1 ) Oversizing the HP can make it run a little quieter, but id discount thoughts of the 14 & 16kW models and they're very big.


2 ) Not sure if this is present or future tense? 2 tanks? 1 x DHW + 1x Buffer? Is your DHW tank an UVC? Please be clear on what you already have and what your considering.


3 ) If you have PV then the HP is already running off PV ;) PV will lend itself to whatever is drawing from the consumer unit unless it has been specifically made divisible by a PV diversion device / other. 


4 ) With a buffer tank you can then do pretty much whatever you like with the HP. Running it for DHW will see it max out, so lower CoP and possibly noisier in operation for that period of high grade heat demand. 


5 ) If its an UVC then this point is moot, as there is very little volume in the HP UVC coil, so no. Better to use excess PV to heat DHW first, and then the car last. Some choose to charge the car off off-peak electricity at night as its out of phase with DHW / sunshine. Pointless having a charged car and no hot water, plus vehicles are typically used during the day so best to have it charged for the morning ready to use ?


6 ) Get a new, more energy efficient family ASAP. Gumtree or eBay etc. 


7 ) If thats a fact, then consider utilising battery storage to run the HP at night, but prob best to wait a couple of years for the battery market to become a but more viable. Prices are dropping, but let them drop a bit more first, IMO. From what I've heard the Tesla cannot be stopped from taking grid electricity to satisfy its recharge requirement, and there are others around which are preferable. I'm looking into this in depth at the moment for a couple of clients, I'll add what I learn when I can. I am not an expert on this by any means. 


8 ) Same here and feel your pain.


9 ) With the windows left open and the HR turned off you'll need all the help you can get ! 


10 ) Pretty fine figures for a retro-fit. Do you have a concrete slab to put heat into or thin screed / other as the main emitter ? With a HP you should be able to top that up without any tears, plus with the extra PV you may well be able to store some excess into a Sunamp heat battery and then leave the HP off at night. Problem is, those open windows, so prob best just to use the HP and be happy with the offset of the running cost via CoP. 


11 ) Maybe reconsider point 6


12 ) Agree. Battery storage or a better medium for storing DHW, other than wet tanks, ( eg a Sunamp heat battery which would give you 3 times the storage of heat energy for the same equivalent physical size but with far lower standing losses ) may become your friends. You don't want to get into a situation where you have paid for additional PV but then are exporting. Get your heating installed and DHW running via the buffer ( from the HP, so all DHW preheat is at max CoP ) and then wait on a years figures before deciding to add more PV. Storing off PV in the day plus the CoP may make more PV an unwise choice unless you can routinely charge the car in the day  


Plenty of info here if you'd like to browse a little.  


For the benefit of others wanting to comment, can you give a better breakdown of EXACTLY what you have in place right now please :) Cylinders / type etc. 



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@Nickfromwales..... That's the longest post you've ever written. Have an honorary PhD.  (Doctorate)


All that's needed for the award of a full-on PhD would be a comprehensive set of references, and a Contents List. And a Viva Voce meeting ( Oral defence of your writing). 


Doctor Nick: has a certain ring about it, no?

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34 minutes ago, recoveringacademic said:

@Nickfromwales..... That's the longest post you've ever written. Have an honorary PhD.  (Doctorate)



I think possibly the longest post he’s ever made was the one to test my rogue heating system ?. It was all good though as every test proved that my system was indeed mince! He should have written up the resolution as that would indeed have been a post worthy of awards. 

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Reply toNickfromwales

Thanks for that Nick.


In place right now:

  • Saunier Duval F35E gas boiler - pre-retrofit combi connected to retrofit UFH 200mm concrete with 70mm tiled screed
  • 7.5 kW PV diverting by 2 Immersuns. Immersun1 to 200L DHW direct tank1 with top and bottom immersions. Immersun2 to 200L indirect DHW tank2 with bottom immersion (original pre-retrofit tank still connected to boiler). The two tanks are connected serially. Tank1 top immersion is on time switch - the other two taking from the Immersuns. All unvented.
  • EV for local trips 5,000 km/year drawing from wall charger.
  • Attached 2017 energy report
  • She Indoors is hobby user of all types of washing machines (3 clothes washing machines, 2 clothes dryers, 2 floor washing machines) - compared to 1 shaver. She often uses 50kWh/day.

Previous points

  1. Pre-purchased Daiken indoor wall-hung hydrobox EHBH16CB3V, user interface EKRUCBL2C, hot water cylinder EKHWS(U)200A3VB - all new kit from discontinued project, but no warranty I expect. This kit can be matched with 11kW, 14kW or 16kW outdoor unit. HWC has an indirect coil and heater.
  2. Present tense - see above
  3. I understand. My question related to possible  power vagaries if feeding HP directly from battery storage.
  4. Ok
  5. Good. Unvented, so leave existing DHW set-up. Install new diverter switch configured for car (Zappi?) - car is at home during day. Dont consider off-peak until get better handle how to get to zero on meter with flexible diverting.
  6. Mother-in-law (nice lady) standing in 20 degrees in front of HR outlet delivering 12 degrees declares to all and sundry 'this is air-conditioning making us cold'. Instructs daughter to switch off system and open windows to get 'fresh air' (uncontrolled and unfiltered) at 6 degrees.
  7. Yes, time was good few years ago to install PV, now good time for HP, but not yet for PV Storage. Look forward to hearing about your progress. 
  8. I lost that battle - now they just say no need for heating, and by definition HR.
  9. ditto
  10. 65% of floors (all GF) is 270mm tiled concrete. I prefer to wait for better batteries (not bring in Sunamp) and stay with that. Might try positioning outdoor unit under a bedroom window.
  11. Yes. I grew up in a house with an open fire. Our parents and grandparents got by ok with woollen sweaters. All this kit is a madness, as you said - but passive-standard building envelope is not.
  12. Yes, got all that. Will install HP next month leaving flexibility regarding DHW - then wait and watch for a year. There has to be a next stage with more PV and storage - see attached import/export balance.

Just wave to us minions as you pass.Scan 2018-8-20 15.23.55.pdf



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