My ASHP Journey in Bonnie Scotland.

12467

Comments

  • cannugec5
    cannugec5 Posts: 433 Forumite
    First Post Name Dropper First Anniversary Combo Breaker
    Well, my first (monthly) ASHP electricity bill is £210. 
    That is actually not so bad as I feared despite it being early autumn and very mild weather. 

    To put it into perspective our summer electricity bill had been about £150 a month. But over the past couple of years our oil bills had averaged £100 a month in addition ( albeit with leakage but we didn’t know that!). 

    I am aware that I’ve used the tumble dryer more this month. Previously it was only used a few times a year, as I dry outside when I can and indoors on a rail when I can’t. But I was warned the new heating would not support indoor drying. However I’m not so sure. Obviously not hanging things over radiators, but surely if the room  is reaching the desired temperature then the drying rail should be just as effective as before? Anyway this week , if/when it rains I will try. ( Drying rail is just that - an unheated  rail). 

    I was questioned in another thread why I’ve put the central heating on so early ( that was written about a week ago when we were still in September). I didn’t reply there so as not to derail someone else’s thread. But the fact is we are in Scotland and the heating is scheduled to keep the house at 20.5 ( was 21) downstairs and 18.5 (was 19) upstairs. So it will have come on when the temperature drops  regardless of the date! Outdoor temperature today was iirc 14 degrees. I am pleased to see that the heating has not been on at all upstairs (yet) which means the insulation must be effective. 

    I have been proactive and increased my direct debit with Octopus before they have asked me to. 
  • cannugec5
    cannugec5 Posts: 433 Forumite
    First Post Name Dropper First Anniversary Combo Breaker
    Today we visited family (Del) who had an ASHP installed a couple of years ago. They went from storage heaters to ASHP and had no end of problems with getting sufficient hot water and warm enough house. To be honest their experience had put us off, but at the same time I was aware that their home is, to us, far too hot, and their use of hot water frivolous.

    So I don’t entirely trust any of their experiences. 

    But today I was intrigued by Del’s  description of the “boost” function.  He uses this, he claims,  if they get home and the house isn’t warm enough. But my understanding is that an ASHP is in such “slow motion” that a boost today would perhaps be felt on Wednesday? Am I wrong here? Can ASHPs produce an immediate and useful boost, or is it perhaps that they can do this at a big cost? Mrs Del suggested that perhaps different ASHPs have different abilities to boost? 


  • The only boost function we have (Mitsubishi Ecodan) is for the hot water.
  • QrizB
    QrizB Posts: 13,822 Forumite
    First Anniversary First Post Photogenic Name Dropper
    cannugec5 said:
    But today I was intrigued by Del’s  description of the “boost” function.  He uses this, he claims,  if they get home and the house isn’t warm enough. But my understanding is that an ASHP is in such “slow motion” that a boost today would perhaps be felt on Wednesday? Am I wrong here? Can ASHPs produce an immediate and useful boost, or is it perhaps that they can do this at a big cost? Mrs Del suggested that perhaps different ASHPs have different abilities to boost?
    I don't know the first thing about Del's ASHP, but if it's set to deliver CH water at 45C but is capable of producing water at 60C with a reduced COP, maybe that's what the boost does? You'd get an extra ~60% of heat output from the radiators, which would quickly raise the air temperature in the house.
    But I'm only speculating here.

    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Taking a break, hope to be back eventually.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • matelodave
    matelodave Posts: 8,606 Forumite
    First Anniversary Name Dropper Photogenic First Post
    Depending on how boost is implemented it will increase the flow temperature with the consequence that the rad will get hotter, the room will heat quicker but it will also have a pretty dramatic effect by increasing the power consumption.

    My unit has the option of adjusting the weather compensation slope up or down by 5 degrees in one degree steps or overriding the weather compensation to a fixed flow temp.

    Normally it idles at around 30-35 degrees but I can wind it up to 50-55 degrees (or even more if I activate the 6kw boost heater - but that really does hammer the power consumption).

    Try to find the COP curves for your HP and you can see how the COP gets worse as the flow temperature is increased
    Never under estimate the power of stupid people in large numbers

  • My unit has the option of adjusting the weather compensation slope up or down by 5 degrees in one degree steps or overriding the weather compensation to a fixed flow temp.

    Exactly the same with me and I have a different make of ASHP to @matelodave.

    ASHPs have a reputation for being slow because they are often coupled with Underfloor Heating.  It's the UFH that is very slow tor respond @cannugec5, not the ASHP. 

    Many gas boilers have a feature called Load Compensation.  This will automatically boost the heating when there is a big difference between the actual room temperature and the temperature set on the thermostat.  Because it's automatic, many users may be unaware of it happening.  This feature is rarer with heat pumps and is only ever possible when the heat pump uses the manufacturer's own room thermostat and not one made by a third party.  With any heating system, the way to achieve a rapid change in the room/house temperature is to oversize the radiators.  The downside to this is that the system may cycle under normal operation.  This is more likely with a heat pump that with a gas boiler because gas boilers tend to have a greater modulation range than heat pumps.  Also the radiators installed with a heat pump tend to be more carefully right-sized than with a typical gas heating system.

    The only other difference I know of only applies to some makes of heat pump like mine (LG).  Mine starts out at a low power output and works its way up to as much as it needs over about 15 minutes.  Gas boilers and other makes of ASHP come on at full output and then modulate down as necessary to stop the return water getting too hot.       
    Reed
  • cannugec5
    cannugec5 Posts: 433 Forumite
    First Post Name Dropper First Anniversary Combo Breaker
    Ok. Next question. 

    I currently have the heating zones set at 17 degrees upstairs and 20.5 downstairs. 

    I recollect the physics of hot air rising (or more accurately transferring the energy in an upward direction). 

    Does the ASHP use the same amount of energy  when on regardless of how many radiators it’s heating? What I am trying to understand is whether there is any economic difference in heating upstairs to reduce the time/ energy it needs to heat downstairs 

    I don’t want my bedroom any warmer but could use the TRV for that purpose. 

    Would downstairs stay warmer longer for less energy used  if upstairs was warmer or does the same amount of heat rise regardless? 

    I think I am perhaps overthinking the whole thing and just perhaps need to focus on comfort rather than so much on economy or I will be a wreck by March! 
  • matt_drummer
    matt_drummer Posts: 1,342 Forumite
    First Anniversary First Post Name Dropper
    Heat pumps do not work anything like a gas or oil boiler and some of the concepts are difficult to get your head around.

    I have a new heat pump installed in June. My performance is OK in terms of efficiency but not as good as it could be.

    It gets complicated.

    Your heat pump will have a minimum heat output it can deliver and your radiators have a minimum amount of heat they can deliver at a certain operating temperature.

    If you stop water flowing through some radiators your heat pump will (probably) produce more heat than the remaining radiators can cope with.

    Your heat pump will shut down when it can no longer get rid of the heat produced.

    You can improve the radiators ability to dissipate the heat produced by the heat pump by turning up the flow temperature.

    Higher flow temperatures are generally less efficient and short cycling is inefficient.

    Ideally you want all the trv's wide open.

    If downstairs is the right temperature but upstairs is too hot then that means you upstairs radiators are too big in relation to those downstairs.

    One solution would be to increase the size of the radiators downstairs so that all of the room temperatures are what you desire when the heat pump is flowing around the whole system.

    This is why I told you zoning was a bad idea. The heat pump needs all the volume of water it can get, otherwise it will short cycle.

    It's more complicated than this basic explanation and it's not really possible to cover everything in a post like this.

    You need to work out what performance you are happy with and how best to run the heat pump. How much time you spend on it is up to you and also depends to some extent what level of data you have.

    It is never going to be as simple as turning room thermostats/trv up and down, that may control the temperature of your house but it's unlikely that this will be the most efficient way to run your heat pump.

    Outright efficiency in terms of COP is not the ultimate aim, the aim is to get as much heat into the house as you need at the lowest possible electricity consumption/cost.
  • matt_drummer
    matt_drummer Posts: 1,342 Forumite
    First Anniversary First Post Name Dropper
    edited 27 October 2023 at 10:29AM
    Here's a rough example of how radiators work.

    If we had a radiator that was rated @ 1,000 watts output at a delta t of 50c and room temperature of 20c

    That means if the mean (average) flow temperature was 70c (typical of many gas or oil boilers) and the room was 20c that radiator would deliver 1,000 watts of energy to the room, it could consume 1,000 watts from the heat source.

    At a delta t of 30c, so a mean flow temperature of 50c and the same room temperature of 20c that same radiator can only deliver about 500 watts of heat to the room. This is a typical design point of many heat pump installations. That radiator can now only absorb 500 watts of heat from the heat pump.

    At a delta t of 10c, so a mean flow temperature of 30c and the same room temperature of 20c that same radiator can now only deliver about 135 watts of heat to the room and it follows that it can now only absorb 135 watts of the heat produced by the heat pump.

    So radiators need to be really, really big to run at low flow temperatures, not just to be able to heat the house but also to absorb the minimum amount of heat delivered by the heat pump.

    If half your radiators are `closed' by the trvs then there is not enough capacity to deliver the heat produced and the heat pump has to turn off.

    If the heat pump is now only flowing water through your downstairs radiators the heat pump will try and put in enough heat to achieve your desired room temperature. Depending on your settings this might involve the flow temperature increasing but you could find that you never get the temperature you want, the heat pump cycles on or off quickly costing you a fortune or that you end up consuming more electricity to heat just your downstairs than you would have done heating the whole house.






  • cannugec5
    cannugec5 Posts: 433 Forumite
    First Post Name Dropper First Anniversary Combo Breaker
    Here's a rough example of how radiators work.

    If we had a radiator that was rated @ 1,000 watts output at a delta t of 50c and room temperature of 20c

    That means if the mean (average) flow temperature was 70c (typical of many gas or oil boilers) and the room was 20c that radiator would deliver 1,000 watts of energy to the room, it could consume 1,000 watts from the heat source.

    At a delta t of 30c, so a mean flow temperature of 50c and the same room temperature of 20c that same radiator can only deliver about 500 watts of heat to the room. This is a typical design point of many heat pump installations. That radiator can now only absorb 500 watts of heat from the heat pump.

    At a delta t of 10c, so a mean flow temperature of 30c and the same room temperature of 20c that same radiator can now only deliver about 135 watts of heat to the room and it follows that it can now only absorb 135 watts of the heat produced by the heat pump.

    So radiators need to be really, really big to run at low flow temperatures, not just to be able to heat the house but also to absorb the minimum amount of heat delivered by the heat pump.

    If half your radiators are `closed' by the trvs then there is not enough capacity to deliver the heat produced and the heat pump has to turn off.

    If the heat pump is now only flowing water through your downstairs radiators the heat pump will try and put in enough heat to achieve your desired room temperature. Depending on your settings this might involve the flow temperature increasing but you could find that you never get the temperature you want, the heat pump cycles on or off quickly costing you a fortune or that you end up consuming more electricity to heat just your downstairs than you would have done heating the whole house.




    I know I’m coming across as really stupid, but I am struggling to understand this.

    The downstairs temperature is easily reached and stays on target all day and night at the constant setting. 

    When you (and others) use the term ‘cycling’ do you simply mean switching on and off? Isn’t that what the pump is meant to do? Surely the alternative is to stay on or off, neither of which will maintain the constant temperature. 

    I do ( I hope) understand what you say about the upstairs radiators not using up the produced heat and therefore causing the pump to switch off. I think I might experiment with putting the upstairs thermostat the same as downstairs ( except in our own bedroom). That will ‘switch on’ an extra 6 radiators. 
Meet your Ambassadors

Categories

  • All Categories
  • 343.1K Banking & Borrowing
  • 250.1K Reduce Debt & Boost Income
  • 449.7K Spending & Discounts
  • 235.2K Work, Benefits & Business
  • 607.9K Mortgages, Homes & Bills
  • 173K Life & Family
  • 247.8K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 15.9K Discuss & Feedback
  • 15.1K Coronavirus Support Boards