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Slash Your Heat Pump Bills Overnight

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(@ken)
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As a homeowner and a seasoned heat pump installer with over 15 years of experience, I've come to a critical realisation: chasing the highest Coefficient of Performance (COP) and Seasonal Coefficient of Performance (SCOP) isn't always the path to the most cost-effective heating system. Instead, it's about being shrewd with the resources at hand. The quest for super efficiency can often feel like a pursuit reserved for the few who own a passive-style, superbly insulated home. But what about the rest of us?

Let me share a personal insight: my house is your average home. Despite my expertise, achieving a heating cost of £1 a day with my heat pump remains elusive. The perfect blend of insulation, solar input, and battery storage needed to attain that super COP/SCOP isn't part of my reality.

Here's my strategy: I exploit cheaper electricity tariffs to run my heat pump more intensively, then dial it back during peak tariff hours. It's a balance of economics over efficiency. For instance, heating water to 60 degrees overnight when electricity costs less may lower my COP, but the kWh price is right. The water stays warmer for longer, potentially sparing me from a pricey reheat during the day.

This tactic extends to home heating. I preheat my house at a higher flow temperature in the wee hours when the tariff hits rock bottom. Sure, my system's COP takes a hit, but my bank account thanks me.

Take a look at the figures I've laid out:

  • At a low rate, the cost of running my heat pump with 10 kWh input is just £0.90, while at a high rate, it jumps to £3.50.
  • As I increase my kWh input, the cost savings between low and high rates become even more pronounced, doubling with every additional 10 kWh.

It's crucial to understand that not all heat pumps can gracefully modulate to the whims of changing seasons. And, frankly, the COP/SCOP is a metric that doesn't translate uniformly across all homes, affected by varying ambient conditions and the specific characteristics of each heat pump.

In my professional journey, I've never seen a better time to install a heat pump. They've evolved to be incredibly quiet, reliable, and sophisticated—truly ready for the future. Yet, I must admit, the current regulations haven't kept pace with these innovations, often making installations more cumbersome than necessary.

In conclusion, while a high COP/SCOP is admirable, it's not the be-all and end-all for everyone. By leveraging cheaper electricity tariffs and managing your heat pump's operation times, you can achieve a harmonious balance between efficiency and economy. This is how I've optimized my system at home, and it could very well be the approach that works for you too.


   
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(@hughf)
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The only things that matters to me - 1. It doesn't cost more to run than the gas boiler we replaced, 2. The house is as warm or warmer.

We've succeeded on both counts. Warmer house, doesn't cost any more.

Nothing else matters... Don't know what my COP is, don't really care.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.


   
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(@andris)
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I absolutely agree! I made huge savings since cheaper tariffs were avaliable at night. I shift just like you. Push it a bit harder when it is cheap. 

This is one of the reason I am so glad we oversized our heatpump a little. I push it hard over a short period. Only need to heate once and the house stays warm throughout. My house is around 21-23c all day. 

16kw Samsung TDM ASHP. 8.4kw PV, power optimizers 20×420watt panels 6kw SolarEdge inverter.


   
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 mjr
(@mjr)
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Posted by: @andris

I made huge savings since cheaper tariffs were avaliable at night.

I'm saving even more since switching to a tariff with a cheap rate in the early afternoon, with less of the disruption of the home getting too hot while I'm asleep.


   
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Majordennisbloodnok
(@majordennisbloodnok)
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In an ideal world, we still have to look at efficiency as well in order to avoid the "my comfort is paramount and the climate be damned" attitude. However, one needs to be in quite a privileged position to be able to follow a route that is the best environmentally but costs more. As a result, I wouldn't feel comfortable criticising anyone for finding a compromise that responsibly balances cost and efficiency.

But the key word there is balance. The situation @ken-bone has outlined seems to me eminently sensible and reasonable; after all, electricity is cheaper at certain times for a good reason and making use of it during those times instead of peak times has its own altruistic benefits.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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Abernyte
(@abernyte)
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Those of us who inhabit the Twilight Zone where a smart meter signal has yet to arrive (along with 2G,3G, and 4G signals) must pursue efficiency and lower costs by a different route. I agree that fixation with COP and SCOP does not help so being imaginative with avoiding the coldest periods for boosting the HP's work load is key, that and a large heat pump!


   
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 mjr
(@mjr)
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Posted by: @majordennisbloodnok

In an ideal world, we still have to look at efficiency as well in order to avoid the "my comfort is paramount and the climate be damned" attitude.

Isn't cost on a time-of-use tariff now partly a representation of how renewable the electricity is at that time? Being more efficient but using more electricity from coal power stations is probably worse for the climate.


   
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Majordennisbloodnok
(@majordennisbloodnok)
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Posted by: @mjr

Posted by: @majordennisbloodnok

In an ideal world, we still have to look at efficiency as well in order to avoid the "my comfort is paramount and the climate be damned" attitude.

Isn't cost on a time-of-use tariff now partly a representation of how renewable the electricity is at that time? Being more efficient but using more electricity from coal power stations is probably worse for the climate.

Absolutely, hence the "as well as". But you're right; it's not just about efficiency any more than it should be just about cost. Once again, the right balance is the key.

 

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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cathodeRay
(@cathoderay)
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Another point to consider: what happens if time of use tariffs become commonplace, and many more people time their electricity use according to their tariff? What if demand in peak periods falls, and rises in non-peak periods? Given the fact an ASHP will be the major electricity consumer in most settings that have an ASHP, shifting their use to off-peak periods might substantially reduce peak load and increase off peak load, and in so doing remove the basis for time of use tariffs...

Domestic energy use is second only to transport use, and much of that domestic energy use will be used for heating:

image

Source:

 

Midea 14kW (for now...) ASHP heating both building and DHW


   
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(@sunandair)
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Posts: 345
 

Posted by: @ken

It's crucial to understand that not all heat pumps can gracefully modulate to the whims of changing seasons. And, frankly, the COP/SCOP is a metric that doesn't translate uniformly across all homes, affected by varying ambient conditions and the specific characteristics of each heat pump.

Sorry, I have to say this post simply serves to muddy the waters. 

I agree that the time of use tariffs may produce savings as a tactic. But in no way can it be seen as a replacement for efficient installation and commissioning. And latterly efficient operation through low and slow heating strategy. TOU tariffs are not a strategy they are a possibly short lived tactic which is a good overlay after the system is set up properly.

lm sure you have good intention but I can see an audience who may wish to exploit this kind of scenario. There is no way I want to see another substitute for proper installation being created by simply telling the customer “just use better tariffs”.

Likewise the manufacturers need to stop piecemeal development of controls with ad-hock   upgrades which aren’t user friendly. 

So I see efficient use of TOU tariffs as a good overlay once efficiency of the overall heating system is achieved. Then you probably will have discovered that’s boost overheating is not efficient or necessary.

but you’re right... CoP is not King.... Efficiency is King.


   
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(@jamespa)
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Completely agree good installation is mandatory.

I think its highly likely that ToU tarrifs will persist, they have, after all, been around for at least the last 50 years!.  They are an obvious way to smooth demand.  This reduces the peak, which in turn reduces the (expensive) network capacity needed and any residual need to burn fossil fuels which, unlike most other ways to generate electricity, can be turned on or off easily.

They may well get more sophisticated and less attractive as night time charging of electric cars begins to become significant thus helping with the day/night balance, but I cant see a way to manage demand without ToU tarifs of some type. 

 


   
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(@davidalgarve)
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467 kWhs
Joined: 7 months ago
Posts: 38
 

The maths attached to a cost analysis of this approach sounds daunting. 

It seems to me that there are two variables that would need to be evaluated, i.e,

1 How much cheaper is the night time tariff than day time?

2 What is the difference between Daytime & night time temperatures? Surely it is cheaper to extract heat from warmer air?

I am trying to hedge my bets by mainly heating DHW up at night, but having an additional period at the hottest part of the day. 

Then again, I am in the Algarve, so temperatures and night time tarriffs are different to the UK


   
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