Major Concern with Heat Pump Technology
We would like to start by saying, we support heat pump technology and they can work well. However, the issue is less with the capability of the technology and more about how it’s being rolled. There are 4 key points that need to be addressed by the industry and government to enable the mass rollout of this product, in both logical/suitable deployment and government grants.- Where can different types of heat pumps be used across the UK?
- How is the heat output of the heat pump measured against low winter temperatures?
- What degree of heat pump oversizing is required to cater for extreme colds/flash drops in weather conditions?
- How is this related to emitter (radiator) requirements?
Myth 1 - Are radiators in our homes oversized enough for heat pumps?
No, they are not. The level of oversizing has to relate to the flow temperature and COP for a heat pump. For example, a heat pump may say this for a COP: A-7/W35 Radiators are sized for heat outputs based on Delta, with Delta 50 being the current industry standard (it shouldn’t be, but let’s park that for the moment). Delta 50 represents a non-condensing gas boiler with a water flow temperature of around 80°C. A COP of A-7/W35 is a water flow temperature of 35°C when it is -7°C outside. If you have a 500 Watt room heating requirement and you want to achieve a COP of A-7/W35, your radiator would have had to be installed with a heat output of about 3200 Watts at Delta 50. If you wanted A-7/W55 COP, your radiator would have had to be installed with a heat output of about 1500 Watts at Delta 50. Unlike everyone else who is just going along with the “radiators are already oversized” notion, we actually have done the research, which you can read about on our “Are Radiators Oversized" blog.Myth 2 - Radiators can’t work with heat pumps?
Yes, they can. The second law of thermodynamics tells us that provided a radiator is appropriately sized to its expected internal flow temperature and external weather conditions, it can heat the room. The size you need is based on this calculation for your home and geographical area. Notions of a “lukewarm radiator not being able to heat my home” were resolved in 1850 when Rudolf Clausius and Lord Kelvin published their statements on the second law of thermodynamics, which were subsequently refined over the last 170 years. Again, here is our proof of this statement “Can Heat Pumps Work with Radiators”.Myth 3 – I can use the COP or SCOP listed on a heat pump to calculate my expected heating costs?
COP – not on its own you can’t. SCOP – you definitely can’t. A COP is a representation of energy usage for a specific condition, how likely that condition is to come about depends on your geographical area. A SCOP listed on a heat pump, which is a seasonal COP, has no bearing to anyone as this changes quite significantly over the landscape of the UK. You use the COP on a heat pump model as a variable required to calculate what your costs will be, you can’t average multiple COPs without weighting them. Below is our relationship between COPs and the Energy requirements of an example home. The home was rated at 8KW when it was -1°C outside with a target room temperature of 20°C.
As you can see, as the COP lowers, the heat energy requirement rises. Therefore, in order to use the COP we need to know the rough local weather conditions and weigh it appropriately. To get an idea of bill prices rising/lowering, we have to compare it to our current system in place. So the data can be used, but all of these factors need to be accounted for, you can read more about this in our “Is the COP on a Heat Pump Accurate?” blog.
Myth 4 – Heat pumps cannot heat my home
This is false. In simple terms, they work exactly the same way as a fridge/freezer does. We think of a fridge/freezer as cooling down/freezing our food. How we need to think of it is that the fridge/freezer is removing heat from the reservoir (the inside of the fridge/freezer) and dumping it in our room. So a fridge/freezer actually heats up our room while making food colder. A heat pump is simply taking heat from the outside world which is a much larger pool of energy, and dumping that into our home. Rough history of science timeline:- 1850 – Lord Kelvin and Rudolf Clausius publish their statements on the second law of Thermodynamics, which tells how heat naturally moves based on the temperature difference between two environments, the bigger the temperature difference, the more energy can transfer.
- 1854 – First commercial ice making machine was made.
- 1913 – Home refrigerators were available.
Available internal energy from heat pumps vs outside temperature
This is where the illusion of choice starts to fade away. So we had a sample home under the following conditions: External Temperature = -1°C Internal Temperature = 20°C Energy Required = 8KW for the entire home In our minds, we would possibly conclude that a 12KW heat pump provides us with enough of a buffer in energy requirements, but let’s explore this and look at the below Panasonic example. 
So what is likely to occur on this heat pump? Well if it ever did get as low as -7°C outside, we can expect that we would need a higher internal water temperature. This is because the heat energy requirement represents our energy output from emitters at any given condition. To meet this higher energy output we either need larger radiators or a higher boiler flow temperature. Therefore, when it is -7°C outside, we could reasonably expect our water temperature to need to be 55°C. This Panasonic product is listed as 12KW on the materials but will only provide 9.6KW of energy in this scenario. The following table demonstrates the relationship between inside temperature requirements and available heat energy from the heat pump as outside temperatures change. 
This chart is assuming that if we require an internal flow temperature of 55°C, we still need this temperature if it does drop to -15°C. But if that were the case, our internal water temperature would need to be higher, and our available energy from the heat pump would drop again. But let’s assume it only needs 55°C flow temp, based on the energy available and the requirement of the home, what would my internal temperature be? It would be 7°C. Because the energy required to raise the temperature of my example home from -15°C using the energy available from the heat pump is around 8.4KW. There are 2 possible things that could be done to raise this: Shut off internal rooms – this however increases the energy requirement of any remaining room radiators. I could possibly raise a room or 2 to safe liveable conditions, but the rest of the rooms would be very cold. Raise the water flow temperature - but the energy doesn’t exist to actually achieve this and the heat pump may not actually have a high enough flow temperature to achieve this. Now it is easy to say that you should have had both bigger radiators to achieve higher heat outputs at lower flow temperatures, and a much more oversized heat pump to ensure the energy available could cater for these scenarios. It is also easy for the heat pump side of the argument to say that these temperatures are rare, but that is really a gas boiler argument when it comes to sizing, as you have the ability to up the flow temperature a lot more. But there is still a similar requirement for Gas Boiler oversizing to cater for extreme colds. So what we have to do is be realistic in our approach and remove any smoke and mirrors around choice.
Do I have a choice between air source and ground source heat pumps in 2023?
We want rules of thumb in the industry to make choices for consumers easy. So, while it would be possible to have Air source in, say, the highlands of Scotland, it is an uncommon scenario. You would need a very new, very well-insulated property to achieve the oversizing required for the radiators to achieve outputs to cater for extreme colds on low water flow temperatures, and reasonable air-to-water heat pump sizing. Therefore, our rule of thumb for the Scottish Highlands is, no, you can’t have an air-source heat pump. You require a ground source heat pump as ground temperatures fluctuate less in extreme colds and generally have the ability for a higher flow temperature to increase radiator heat output. On the other hand, If you live in Brighton, you do have a choice. As long as you oversize air-source heat pumps appropriately and your radiators, to cover extreme colds that far south. We hit -15.2°C this year in the Scottish Highlands, so while you may not account for that rarity when it comes to operating cost, you do need to for actually functioning and providing a safe and healthy environment. As far as what works between Brighton and Scottish Highlands, the practicality of the current solutions and what choice you realistically have is dependent on how far north you go.What other considerations are there for a rule of thumb?
Property age. The older the property, the higher the energy requirement per Square feet, the bigger the radiators required and more of an energy buffer will be needed. This is true even when you add insulation, so a well-insulated property built before 1985 will have a higher heat loss per square feet than a property built after 2013. So you have less availability of space for larger radiators. Property type is also a further consideration. Detached vs mid terrace, Grade listed vs modern property. So if you had a grade 2 listed building in Brighton, your rule of thumb is a ground source heat pump. Uninsulated single brick or double brick, given the cost of insulation and the limitation of radiator space to achieve a decent COP and manage energy requirements for extreme lows, it could be a choice, but on a case-by-case basis, it could be quite likely you need a ground source. But everything else in Brighton is Air Source, ground source wouldn't be a choice. In the highlands of Scotland however, Air Source with a property built in 2013 or after could be a sound choice, but outside of that, it would be a significant risk to not have a ground source. If we consider my approach to this problem, it is not all doom and gloom, we aren't all going to die from the heat pumps approach, it is just common sense. Some of this may already be considered by installers and heat pump professionals, which will change installer to installer. But we know for certain that it is not considered in the current grants - how is it in any way fair that the grant is the same amount for those living in Brighton and Scotland, considering that your installation cost is always going to be higher in Scotland than Brighton as even your air source heat pump in Scotland for a property built post-2013 is going to need to be oversized compared to a like for like property in Brighton.Any other considerations for this?
When we couple this problem with COPs as well, it probably isn’t fair that the post-2013 property in Scotland has an Air source heat pump when the like-for-like property in Brighton has one as well, as the COP and SCOP will be very different. The person in Brighton will spend less on energy than the person in Scotland given the relationship between lowering temperatures and energy requirements, we cover this in the “Is the COP on a Heat Pump Accurate?” blog.Considering geographical and property type concerns together
Well as we have demonstrated, using available examples and a bit of common sense, there is nothing wrong with the technology, it is just we don’t acknowledge the limitations of it given the changing landscape of the United Kingdom. One argument against what we have above is how well these work in Scandinavian countries, but you can bet that Norway with a dwellings total of 2.5 million (less than 10% of the UK) had more flexibility around this given their, on average, higher GDP per capita than the UK. So while Scandinavian countries prove the technology works for the UK, it doesn’t reflect our approach which has to be very different to cater for and work with the UK's range of dwellings. We would need:-
Defined standards of what should be deployed per geographical location in the UK, including oversizing requirements and extreme temperature requirements.
- Scotland and Islands
- Northern Ireland
- Northern England
- Midlands
- Wales
- London and South-East England
- South-West England
- Southern England
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Broken down into property age, type and construction:
-
Pre-1985
- Uninsulated Single Brick
- Uninsulated Double Brick
- Uninsulated Cavity Wall
- Insulated Single Brick
- Insulated Double Brick
- Insulated Cavity Wall
-
Post-1985
- 1985 – 2000
- 2000 – 2013
- 2013 onwards
-
Pre-1985
- Grants and Subsidies to reflect a realistic choice available to the consumer.
