Posted by: @heacol

↑

If you want some evidence, just look at the report I published here, a rise from 36 to 48 Deg C incurred a running cost rise of 76%, as this gets worse as the flow temperature increases, I estimate the increase from 45 to 50 Deg C Wil incur a rise of the 40-70% mentioned.

I note from YouTube reviews of installations that British Gas seem to have no problem with designing for a 45c flow temp in their specs. 

@jamespa octopus offer is a fixed price so if their survey says you need 6 rads then they are included and shouldn't change the price. Where it had indicated a rad change the app might suggest a type 21 was sufficient but the surveyor was happy to override and put a type 22 and change dimensions as well. He wasn't able to add additional radiators above what the survey flagged as inadequate at their design temp.

Posted by: @heacol

↑

@jamespa If flow temperature was the only variable, you may have a point, however, there are tens if not many hundreds of variables that need to be taken into account, I am only getting to grasps with a few of them, I have a long way and probably will never understand all.

If you want some evidence, just look at the report I published here, a rise from 36 to 48 Deg C incurred a running cost rise of 76%, as this gets worse as the flow temperature increases, I estimate the increase from 45 to 50 Deg C Wil incur a rise of the 40-70% mentioned.

Thanks, however the link to the report didn't seem to be present.

Posted by: @gunboatdiplomat

↑

@jamespa octopus offer is a fixed price so if their survey says you need 6 rads then they are included and shouldn't change the price. Where it had indicated a rad change the app might suggest a type 21 was sufficient but the surveyor was happy to override and put a type 22 and change dimensions as well. He wasn't able to add additional radiators above what the survey flagged as inadequate at their design temp.

OK so that's not so bad.  Basically the rads you are paying for (or which are bundled) will likely end up a oversized for 50C if you insist on 22s and next size up throughout.  Those they don't change you aren't paying for, so you haven't actually lost anything (apart from the VAT relief).  Good chance therefore that if you change some of those that are currently just good enough for 50C (and therefore that they don't change) you will be able to turn down the FT.

In fairness to Octopus their costings presumably assume a maximum number of rad changes (by the sounds of it more or less independently of the rad spec).  You cant expect them to go much (or any) above this without paying more.  So the best you can do is to push their 'envelope' as far as it will go, ie ask for larger capacity in the rads they do change than is strictly necessary for the design temp (within reason of course).  Because of their (simplified) pricing, this becomes a game which you can play without feeling guilty.

Again all only if the pump capacity issue is first sorted, and all assuming that their design is fundamentally sound (which, to first order, = simple as @derek-m says).

Also of course only after seeing what the BG competition has to say!  More quotes = more information and more options.

This is where a few hours with heat punk or similar to do your own room by room heat loss and then know what you might need to tweak above and beyond the octopus design is well worth the time!

Posted by: @gunboatdiplomat

↑

@lucia if you think the heat pump size isn't right it's definitely good you are getting a second opinion with BG. I did my own room by room heat loss with heat punk which was hugely useful to compare against. 

I'm not sure bigger rads will solve a really undersized pump - if it's too small to meet the heat loss on colder days it just won't be able to heat the house? I guess it might give you a bit of headroom if the pump has a slightly higher capacity at 40 or 45C Vs 50C in colder weather.

Absolutely, that's what I think too. I keep starting with Heat Punk but I need to go back to check all my measurements again.

But so far, all my actual data, the infra red heat loss photos I took from inside and outside last winter, my whole year metered gas bill (heating only) run as a Podesta calc, and my one very exposed wall on a hill (so exposed it had to have new wall ties last year), ancient windows etc., all indicate 4kw isn't enough.  

Also, the modulation range of the 4, like the 9 is not good. (Dunno if the 6 is much better on that score though). Daikin are really difficult to get detailed tech info from. 

Posted by: @jamespa

↑

OK so that's not so bad.  Basically the rads you are paying for (or which are bundled) will likely end up a oversized for 50C if you insist on 22s and next size up throughout. 

The lead installer told me the 50c design temp was precisely to keep down rad changes. They offer a fixed price quote before they see your property based on very vague tick boxes and this says 'all radiators included'. 

But there's quite a few other people's quotes and specs online - and the variations in them appear to defeat any logic.  It's bizarre. 

Whatever happens they don't reduce the quote. You can't 'insist' on anything during the survey because it's a 'computer says no' situation with the heat loss software. It won't let the surveyor go freehand so to speak. 

But he can take notes and my lead installer (who came to check a possible water tank location) agreed with my take on things, looked at my infra red photos in amazement and thinks I should try pushing back when the printed spec comes through..  

Watch this space.

Posted by: @lucia

↑

Also, the modulation range of the 4, like the 9 is not good. (Dunno if the 6 is much better on that score though). Daikin are really difficult to get detailed tech info from. 

Anecdotally it looks like the 4/6/8 Daikin can get down to 280W minimum power input: https://community.openenergymonitor.org/t/performance-of-9kw-daikin/25243/23

If the COP is say 5 in milder temps with a lower flow temp that might mean a minimum output of approx 1.5kW. If that is lower or close to  your expected heat loss for most of the year even at milder temps maybe the 'oversizing' due to the 4/6 unit being actually an 8 isn't  a problem.

Posted by: @gunboatdiplomat

↑

If the COP is say 5 in milder temps with a lower flow temp that might mean a minimum output of approx 1.5kW. If that is lower or close to  your expected heat loss for most of the year even at milder temps maybe the 'oversizing' due to the 4/6 unit being actually an 8 isn't  a problem.

Thanks for that it's helpful and it makes me feel better about the Daikin. 0.28 Kilowatts as a minimum is cope-able. I think. 

My problem in thinking this stuff through is I have no confidence in my own understanding of varying outside temps & my heat loss when it's just average English blah weather. I've got a lot to learn. 

Posted by: @editor

↑

because the heat pump unit is so expensive to replace.

But that isn't really correct. You can pick up a good ASHP from the likes of City Plumbing for £2 to 2.5k. once your system is there it's no different to replacing a good boiler.

Posted by: @lucia

↑

Posted by: @gunboatdiplomat

↑

If the COP is say 5 in milder temps with a lower flow temp that might mean a minimum output of approx 1.5kW. If that is lower or close to  your expected heat loss for most of the year even at milder temps maybe the 'oversizing' due to the 4/6 unit being actually an 8 isn't  a problem.

Thanks for that it's helpful and it makes me feel better about the Daikin. 0.28 Kilowatts as a minimum is cope-able. I think. 

My problem in thinking this stuff through is I have no confidence in my own understanding of varying outside temps & my heat loss when it's just average English blah weather. I've got a lot to learn. 

I think the best that can be obtained from assessment is the approximate heat loss, since the actual heat loss will vary with changing weather conditions, even when the Inside Air Temperature (IAT) and Outdoor Air Temperature (OAT) remain the same.

Extensive tests and observation have shown that the instantaneous heat loss can vary quite considerably over a 24 hour period, with the greatest heat loss often occurring just before dawn.

In its most basic terms, a heating system consists of some form of thermal energy generator pouring thermal energy into your home, which in turn leaks out. Just as water flows down a slope (unless prevented from doing so), thermal energy will flow from a higher temperature to a lower one.

A home heating system can therefore be represented as a number of open vessels, each connected together using pipework of varying diameters, with the heat source pumping thermal energy into the first vessel representing the water within the heating system.

I could probably produce a diagram to demonstrate this analogy if you wish.

This measly sheet is all I could find data-wise. It tells me nothing. And the model is EBLA04 -08 and the Octopus pumps are EDLA04-08

I don't know why Daikin are so cagey about specs - they're one of the biggest and oldest manufacturers. I might ring them tomorrow and ask... 🙁