This Glen Dimplex Heating & Ventilation sponsored CPD explains how to specify hybrid electrical heating systems to achieve lower energy use and emissions for buildings
Governments around the world have committed to reducing carbon emissions and are legislating to that end. In the built environment, designers and developers are using innovative heating solutions as part of this effort.
This CPD will look at hot water heat pump technologies and the role hybrid electric heating systems can play in helping to lower a building’s energy use – and consequently its carbon emissions. This will be reviewed for new buildings, and retrofit options for existing housing stock.
In 2015 almost every country in the world agreed to become a net zero emissions economy under the terms of the Paris Agreement, which set a 2050 target of reducing greenhouse gasses to 80% below 1990 levels.
The recent COP26 climate change conference in Glasgow threw the spotlight onto the need for action once again. In light of emerging scientific data, the much-discussed net zero ambition has been brought forward to become a legal target by 2050, meaning that current UK legislation and targets are no longer sufficient.
The UK government, in conjunction with the Scottish and Welsh administrations, commissioned research into what measures will be needed to achieve net zero by 2050. The results showed the UK will only be able to achieve the new goal if it commits to significant and immediate regulatory action.
Consequently, each government is looking to update building regulations to set stricter compliance targets on the UK construction industry, including looking at fundamentally changing the way heating, ventilation, and air-conditioning (HVAC) services are both designed into new buildings and used to decarbonise the existing building stock.
What is a hybrid heating system?
The drive towards delivering more environmentally sustainable heating means hybrid systems and technologies are being considered more widely.
A hybrid heating system contains a mix of technologies for space and water heating. These are often, but do not need to be, dual-fuel systems but can also consist of two different technologies working together to supply a dwelling’s heating demand, often with integrated controls. An example could be a heat pump installed alongside a gas boiler, or a hot water heat pump combined with direct acting panel heating.
￼It is for this reason that domestic hot water heat pump solutions are a growing specification in the UK.
They offer flexibility in specification design, while at the same time contributing significantly to carbon and primary energy targets. This allows a designer to utilise a choice of space heating and ventilation solutions. There are various HVAC options available to aid designers in meeting the targets for the compliance metrics for carbon emissions and primary energy.
The benefits of low carbon solutions, such as direct electric panel heaters, are only fully realised in operational use when the fabric retains heat within the building. This metric aims to ensure that such solutions are not used in developments with low fabric performance, due to the current high unit cost of electricity if they are required to run on a constant basis.
Modelling has also shown that where designs comply with primary energy and minimum fabric standards, the affordability target is also met.
Why are hybrid electric solutions part of the route to decarbonisation?
Hot water heat pumps are exceptionally efficient, with a coefficient of performance (COP) rating of approximately 3.0, versus condensing boilers which achieve a maximum COP of 0.9. They are also easier to fit than other low carbon solutions which often require specialist installers. They do not require external space as they are a heat pump and hot water cylinder integrated into one unit, for installation inside homes and apartments.
The cost of a hot water heat pump depends on the manufacturer, but it is comparable with that of a gas boiler. The space heating provision in well-insulated homes can be effectively addressed by installing direct acting electric panel heaters. These are 100% efficient at the point of use.
The technology allows the specification of varied space heaters, such as this electric bathroom radiator.
Modern models are affordable and feature many energy-saving features that help to keep electricity usage low. This also means that a hybrid electric system which combines a hot water heat pump with panel heaters delivers all heating services to a home using electricity, which is beneficial in the move towards zero carbon because of the ever-decreasing carbon factor of electricity in the UK.￼
High heat retention storage heaters (HHRSH) such as the Dimplex Quantum are a great option alongside HWHPs in retrofit scenarios where a medium to high level of space heating is required. They have smart controls that take price signals from the electricity grid, storing thermal energy for space heating when it is most available, cheapest and low carbon.
The Standard Assessment Procedure (SAP) 10.1, published in October 2019, introduced a new carbon factor for electricity of 0.136, versus the 0.210 figure for gas, to reflect the transition from coal-fired power stations towards electricity generated by carbon-free power sources such as wind, nuclear and solar. This carbon factor will continue to decrease as the grid is further decarbonised, meaning the carbon footprint of electrified solutions will be reduced over time until 2035, at which point the electricity grid is expected to be carbon neutral.
As the carbon factor is measured in kilograms of CO2 per kilowatt hour (kg/CO2/kWh) this can easily be translated into how many grams of CO2 are emitted per kWh of heat generated for each fuel. Electricity stands at 136g, with gas at 210g.
This should be considered in combination with the significantly higher efficiency of hybrid electric heating systems when compared with traditional gas boilers, as the cumulative effect of a low carbon factor and high COP (coefficient of performance) make these hybrid electric systems perform excellently when trying to reduce the carbon impact of a building, offering benefits in both SAP and RdSAP for new and retrofit design modelling.
What are the options?
While the Climate Change Committee has advised the UK government of various pathways to net zero, the only consistent “no regrets” option – one which is unlikely to cause any future issues – in the built environment is the widespread application of heat pumps. Alongside the fabric improvement of existing buildings, this “no regrets” option is well proven in other countries and has clear potential to significantly reduce our carbon footprint .
This does not mean every building needs a traditional mono-block air-source heat pump located outside, though – the ability to be technology agnostic is an important factor when considering how an industry can move quickly towards a target. For many buildings, existing and new-build, there are circumstances within which application of a traditional heat pump is either sub-optimal or simply not possible.
Constraints of space, location and funding are common reasons why a traditional heat pump might not be suitable for a project.
Take, for example, a low-rise development of apartments in an urban area. Central renewable plant could be considered; however, this could prove to be a costly and space-hungry solution. Split systems would occupy external building space, which is often limited by local planning regulations.
It is possible to consider instead a solution where the insulation of the building could be the primary recipient of the available funding for the project. A fabric-first approach will reduce the total energy requirement of the building to the lowest possible level.
After this, fulfilment of the remaining energy requirements can be considered, starting with the greatest loads first.
Pros and cons
The primary demand for energy in domestic buildings is the production of hot water. If this could be produced renewably using an in-home heat pump not much bigger than a traditional water cylinder, then the high fabric performance of the example building would require very little load demand for its space heating.
Using direct electric panel heaters could be an incredibly cost-effective way of offsetting the capital cost of the system, providing a well-insulated, predominantly renewable design with no requirement for gas services.
This design is proving to be popular, as it can be easily designed in compliance with the current and upcoming Building Regulations, with hot water heat pumps from major manufacturers being recognised in SAP Appendix Q. With a lower capital cost and more usable space, it is a great option for smaller, well-insulated homes.
One of the arguments often used against hybrid electric systems is the use of direct-acting space heating. Consider again, however, revised carbon factors and that the UK’s electricity generation will be carbon neutral by 2035, and the impact of this technology will be reduced to nothing during the lifetime of the installed units.
The next point of opposition is typically around the load such systems could place on the electrical grid. Even though their use is typically in very low-load scenarios as in the example given, direct acting appliance will draw 1kWh through the meter for each 1kWh needed in the home.
When compared against a heat pump, which may produce 3kWh, 4 kWh or even 5kWh into the home for each 1kWh taken from the grid, these technologies can appear to be a detriment to the electricity grid at a time when transport and other sectors are also trying to electrify.
This viewpoint, again, uses outdated information about how many of these technologies operate. For example, consider the capabilities of these increasingly smart products to provide flexible grid services, as well as to work with smart meters and make use of time-of-use tariffs – in a similar way to electric vehicles. The result is an array of electric appliances of all types which can offset some of the loading and frequency profile issues associated with the wide-scale application of heat pumps onto the supply network.
This principle of electrical diversity is part of the Building Regulations when considering electricity use inside a home, and is fast being recognised as an important supporting factor in maximising use of the national electricity grid, with an array of technologies supporting, offsetting and complementing each other.
While this technology offers significant benefits for new-build schemes, it also works with retrofit projects. Its design and application for refurbishment work can be significantly cheaper and more straightforward than with a traditional heat pump, meaning spare funds could be available for further insulation improvements, recovering additional energy and carbon across the delivered works.
In many applications, a hybrid electric solution which combines elements such as hot water heat pumps, direct acting panel heaters, high heat-retention storage heaters, or similar thermal energy store can increase the benefits to the user, the building and the network.
The government has decided the widespread application of heat pumps is a “no regrets” option for decarbonisation of the UK. It is critically important to offer developers, specifiers, installers and homeowners a choice when it comes to the technologies that they use, and so broad consideration of heat pump technologies and the systems that they are part of should be made to ensure the best possible application of new technologies to the unique requirements of each building, owner and user.
There is no silver bullet to solve decarbonisation and electrification, and the strength of our future energy system will undoubtedly in part be attributed to its flexibility and diversity.
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