Us consumers can help by shifting our usage away from the early-evening period of peak-demand. But you can't do that if your heat-pump has no storage (electric or hot water) with which to keep the space heating 'live'.
and I started thinking.. does hot water in the tank contribute to heating the house in some way that I have missed? As far as I understoof, the ASHP heats the property and heats the water in the tank for showers etc. Is there some cleverness whereby the hot water in the tank is also used to help heating the home? How does one know if their system supports something like this? How does one know if their system is doing so?
Mitsubishi have something called 'smart grid' in the FTC6 controller. This is supposed to use a buffer tank to store water heated at cheaper times and use it at more expensive ones. This is not using the DHW system; I think that would be unwise because you would not want the heating system using all the HW you are just about to have a bath with.
I have no idea if smart grid would work with tariffs available in the UK. I also have a niggling doubt whether adding expense and complexity is a good idea and whether it another example of a solution looking for a problem.
"a heat-pump requires a house with an Energy Efficiency Rating of A or B"
"If your house can’t achieve a SAP-score above 80, then there’s no point considering a heat-pump"
Really?? Have I misunderstood this or is these the same numbers found on the EPC? If I haven't and they are then these statements would be nonsense. My EPC rating is D/60 and my ASHP works very well. I'm sure I'm not the only one without an A/B rating and with a heat pump.
@kev-m I think that’s a fair challenge and has been bought up on that site too, I didn’t write the content, just contributed my experience with the insulation on my system. I was referring to the article for the explanation of the energy storage. I have seen examples of heat pumps working well in less well insulated properties but here I think the trick is to get the operating principles correct and use the fabric of the building to store some of the energy and not allow the building to cool too much, something that is hard on many new builds. However a lower SAP score, although not a perfect assessment, and I believe an EPC is a crude version of this, does indicate possibilities for better insulation which will result in less energy being require to heat the property. Using A/B as a threshold is far too crude. I’m not a building surveyor though so someone more knowledgeable than me would need to explain further.
does hot water in the tank contribute to heating the house in some way that I have missed?
It depends on what tanks and controls have been specified by the installers.
Me-thinks we are giving them too much freedom to design systems with inadequate storage. That means our heat-pumps continue to draw mains electricity at the most expensive times of day. That is unsustainable technically, financially and ethically.
I don't yet have a heat-pump, but I've had a thermal store for the past 15 years. It holds heat energy for both DHW (output at 42°C) and UFH (46°C), and is fed by a gas boiler and a solar-thermal array.
If sites with heat-pumps wish to store energy for space-heating as hot water, then you'll need something larger than the 280-litre thermal store shown above. That's because you don't want to store it at higher temperatures (above 55°C). A heat-pump becomes progressively less efficient as the output temp rises.
One solution is to have a separate cylinder for DHW and space-heating storage:
The diagram shows 'oversize radiators', but lower temperatures would be possible if there was UFH.
Due to the very large size of such a thermal store, the other option to evaluate is battery-storage
This is the strategy for which I'm currently developing a control system.
The controls will be able to take into account a Time-of-Use tariff and/or when there is a high proportion of renewables in the Energy-mix being reported by my DNO.
I agree that improving the fabric is important and that energy storage in the home may work in some circumstances. However, only a small proportion of homes in the UK are, or ever will be, A or B rated and to suggest that they are the only ones where a heat pump should be considered is wrong. It's the sort of messaging I would expect from the gas boiler industry or the climate change denying popular press.
Mitsubishi have something called 'smart grid' in the FTC6 controller. This is supposed to use a buffer tank to store water heated at cheaper times and use it at more expensive ones.
The descriptions I've received from the group of participants on the Zero-Carbon Heating Trial in SE England show that a buffer-tank is a different concept. Some sites do indeed have buffer tanks and they are configured like this:
That diagram is very generic, but the buffer tank is basically there to ensure that the water being returned to the heat-pump is sufficiently low in temperature.
It's a method to ensure that the heat-pump can operate with a 5°C difference between flow and return.
"a heat-pump requires a house with an Energy Efficiency Rating of A or B"
"If your house can’t achieve a SAP-score above 80, then there’s no point considering a heat-pump"
Well I'm the author of that topic on the OVO Forum.
That information about SAP-scores has come from a multi-party video conversation I had in summer'21 with the senior Western Power engineers who co-ran the Freedom Trial of heat-pumps in houses owned by a housing association.
That Trial was funded by the Welsh Government who are several years ahead of England and Scotland in running such investigations. Unlike the three BEIS-funded Trials presently under way in England, Freedom retained the services of the engineering team from Western Power and Wales & West Utilities for the entire duration. They not only oversaw the design and installation, but the entire monitoring and optimisation stages as well. Their report therefore carries considerable weight.
Freedom Project diagram replicated here with permission from Western Power Distribution
You will notice that Freedom tested hybrid heat-pump installations. This was evaluated with normal mains gas at a Calorific Value above 37MJ/m³. However the analysis also allowed them to evaluate the effectiveness of hybid installations using hydrogen at 12MJ/m³.
One of the difficulties with SAP calculations is that they take into account so many variables that are not related to insulation and building-fabric within Part-L of the Building Regulations.
Indeed, adding the heat-pump itself raises the SAP-score significantly even if there is no retro-fitting of additional energy-retention measures. This needs addressing in the next release of SAP criteria which will hopefully coincide with the forthcoming Future Homes Standard of the Building Regs themselves.
does hot water in the tank contribute to heating the house in some way that I have missed?
It depends on what tanks and controls have been specified by the installers.
Me-thinks we are giving them too much freedom to design systems with inadequate storage. That means our heat-pumps continue to draw mains electricity at the most expensive times of day. That is unsustainable technically, financially and ethically.
I don't yet have a heat-pump, but I've had a thermal store for the past 15 years. It holds heat energy for both DHW (output at 42°C) and UFH (46°C), and is fed by a gas boiler and a solar-thermal array.
If sites with heat-pumps wish to store energy for space-heating as hot water, then you'll need something larger than the 280-litre thermal store shown above. That's because you don't want to store it at higher temperatures (above 55°C). A heat-pump becomes progressively less efficient as the output temp rises.
One solution is to have a separate cylinder for DHW and space-heating storage:
The diagram shows 'oversize radiators', but lower temperatures would be possible if there was UFH.
Due to the very large size of such a thermal store, the other option to evaluate is battery-storage
This is the strategy for which I'm currently developing a control system.
The controls will be able to take into account a Time-of-Use tariff and/or when there is a high proportion of renewables in the Energy-mix being reported by my DNO.
Hi,
I can now see why an electricity distribution company is getting involved in home heating system, the primary reason, as far as I can see, is to help balance the grid, by moving some of the demand from the peak period, to periods when demand is lower. Whilst this approach has benefits, in reducing the total amount of generating capacity required, and also limiting the instantaneous load on the distribution system, it does not actually save energy, unless the home system also incorporates solar thermal and/or solar PV systems.
My understanding of what has been described as Smart Grid operation, would be for the grid operator to be able to switch off and on equipment such as refrigerators and freezers for a period of time during peak demand. For the grid controllers to be able to control the charging, and eventually, discharging of EV's from and to the grid to also help balance the system. In relation to heat pumps, some now have the capability for their electrical consumption to be limited for a period of time to also help balance the grid.
"a heat-pump requires a house with an Energy Efficiency Rating of A or B"
"If your house can’t achieve a SAP-score above 80, then there’s no point considering a heat-pump"
Well I'm the author of that topic on the OVO Forum.
That information about SAP-scores has come from a multi-party video conversation I had in summer'21 with the senior Western Power engineers who co-ran the Freedom Trial of heat-pumps in houses owned by a housing association.
One of the difficulties with SAP calculations is that they take into account so many variables that are not related to insulation and building-fabric within Part-L of the Building Regulations.
Indeed, adding the heat-pump itself raises the SAP-score significantly even if there is no retro-fitting of additional energy-retention measures. This needs addressing in the next release of SAP criteria which will hopefully coincide with the forthcoming Future Homes Standard of the Building Regs themselves.
That doesn't change the fact that it's wrong. In order to decarbonise, we need simple and persuasive messaging. Telling people not to bother with a heat pump if their house is not A or B rated is both simple and persuasive, but it is also poor advice.
I know about some of the the shortcomings with the EPC/SAP scores but it's what we have now and we just need to be a bit more careful with what we tell people.
I can now see why an electricity distribution company is getting involved in home heating system, the primary reason, as far as I can see, is to help balance the grid, by moving some of the demand from the peak period, to periods when demand is lower.
If 'Balancing the Grid' were as straightforward as that, then the DNOs could achieve it by reinforcing their network.
However they are obligated to Ofgem under a contract called RIIO-ED1 (shortly to be replaced by ED2). Amongst other matters, the RIIO agreement constrains their revenue unless they take action to reduce network losses.
The vast majority of our domestic properties are fed by a single-phase supply. 100 years ago that was reasonable. A typical local substation serving 100-250 dwellings would be supplying similar loads across all three phases.
Adding PV solar panels and EV-chargers creates long-term additional loading, lasting several hours. These two technologies have doubled losses due to phase imbalance from roughly 5% to 10%.
Heat-pumps are worse however. They 'cycle' at intervals between 30-mins down to 5-mins, depending on how well your installation has been optimised.
Here's snapshot I've just grabbed from an 11kV local substation in an urban area of SW England during today (Mon 23rd Jan)
This graph shows the three phases (L1 L2 & L3) on one of six 440v feeds which serve the surrounding area. Sampling of the average current occurred over 10-minute intervals.
Phase L1 is higher during most of the daytime because houses on that phase have fewer solar-panels.
Phase L2 supplies much more current towards the end of the afternoon as the sun sets and the early-evening peak arrives.
I've shown in dotted lines the 'trend' for both L1 & L2 so you can see them both climbing during the day, but L1 at a steeper rate.
I happen to know that there are several houses with heat-pumps in that area, although it isn't local to me. I suspect that the majority of the fluctuations throughout the day are due to heat-pump cycling. These have been well optimised and are typically operating with longer cycles than most do in the UK.
When phases are unbalanced, as in the above illustration, the 'spare' magnetic flux in the transformer gets wasted as heat.
And that's just a brief overview of phase imbalance. Heat pumps are also notorious for also creating grid-losses by induced harmonics. But that's another story.
Whilst this approach has benefits, in reducing the total amount of generating capacity required, and also limiting the instantaneous load on the distribution system, it does not actually save energy, unless the home system also incorporates solar thermal and/or solar PV systems.
Moving demand loads certainly does save energy... but it's just not visible to us consumers on our smart meters.
I don't work in the energy sector, and have never done so, but I'm gradually beginning to realise how important it is for the UK to move as fast as possible towards Demand Side Response using a smart grid. Too little attention is being paid by us to the daily 'standing charge' portion of our electricity bills which goes towards resolving the horrendous inefficiencies in our Distribution and Transmission Grids.
We need to wake up to this reality regardless of how we feel about Climate Change.
My understanding of what has been described as Smart Grid operation, would be for the grid operator to be able to switch off and on equipment such as refrigerators and freezers for a period of time during peak demand. For the grid controllers to be able to control the charging, and eventually, discharging of EV's from and to the grid to also help balance the system. In relation to heat pumps, some now have the capability for their electrical consumption to be limited for a period of time to also help balance the grid.
Well it's commands being sent from our chosen Energy Supplier which actually switches on/off devices in our homes. That facility can't be done by the grid-operators (DNOs) because they can't access our Smart Meters, not even to check consumption.
The mechanism laid down in the Smart Meter specifications (2013) is for domestic loads to be controlled at our request, and using a feature in the Smart Meter called Auxiliary Load Control Switching (ALCS).
To date I don't know of a single trial which has attempted to use the ALCS facility.
On the road towards a Smart Grid, we have yet to cross the start line. That's appalling.
As an example of this strategy, here's a diagram published 8 years ago by DFES (now BEIS) in a public information booklet showing how electric vehicles will be charged at home:
We are years away from having this implemented. 😥
This post was modified 2 years ago 2 times by Transparent
