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Freedom: the key to carbon, comfort and cost in home heating

Freedom: the key to carbon, comfort and cost in home heating


Passiv, Wales & West Utilities and Western Power Distribution provide an update on ‘Freedom’, a joint project designed to evaluate the potential of hybrid systems to transform the UK’s domestic heating market.

The Freedom Project is investigating the potential of multi-fuel, hybrid home heating systems to address the balance between energy security, social impact and environmental security to deliver comfort, carbon and cost. We are investigating the consumer, network and energy system implications of hybrid heating system deployments, where domestic heating systems have the option of operating using a standard gas boiler, an air source heat pump (ASHP), or both.

The Freedom Project has completed 24 months of a 27-month project programme. The Project has installed 75 hybrid heating systems in a mix of private and social housing, with the focus now on the optimised controlling, monitoring and consumer feedback throughout the 2017-18 heating season.

The remainder of the project will now focus on the optimised controlling, monitoring and consumer feedback throughout the 2017-18 heating season. A full report will be released detailing the consumer, network, carbon and energy system benefits of a large-scale deployment of hybrid heating systems with an aggregated demand response control system.

The global recognition of the challenges of climate change, in particular the ambitious reductions in carbon emissions proposed by the UK Government (i.e. 80% reduction relative to 1990 levels), are driving significant changes across the energy landscape. Significant progress is being made in decarbonising electricity generation and seeking low-carbon gas alternatives.

However, in the UK, domestic heating remains largely unaffected by attempts to lower carbon outputs, aside from the progress made through increased boiler efficiency.


Here is short film about the Freedom Project:

The installation

We have installed a hybrid heating solution in 75 homes – a mix of social and private housing – in and around Bridgend, South Wales. The Freedom Project’s hybrid heating system includes an exterior ASHP, a high-efficiency gas boiler inside the home and a hybrid control panel.

For the first time, this project brings together the gas and electricity network operators in the field trial region and aims to provide robust, field-tested data that can make a meaningful contribution to long-term network investment planning. The cross-sector scope makes this a unique project, which aims to set the benchmark for holistic, ‘whole systems’ innovation.

Designing heating systems that combine gas boilers with ASHPs, while employing smart switching between the gas and electric load, enables the choice of fuels to match consumer demand for heat. This highly flexible approach delivers multiple benefits.

Hybrid heating systems can help householders save money on heating and hot water bills while supporting the shift towards the decarbonisation of heat. Avoiding the use of electricity during times of peak demand – demand side response – will help reduce the need for further investment in generation capacity. It also enables the heating system to take advantage of time-of-use price differences between the two fuels – so-called ‘fuel arbitrage’.


What we’ve learned

Imperial College’s modelling has also highlighted
 a counter intuitive carbon 
outcome. Conventional wisdom is that full 
electrification delivers a lower carbon output to hybridisation; however, this is not always the case. On the coldest days
 when the electricity system 
is under greatest load, or 
when intermittent renewable generation is insufficient to 
meet demand, the additional ASHP load would need to be 
met by marginal increases in flexible generation sources. Flexible generation equates to the use of traditional fossil-fuel power stations, such as coal and gas turbine plants.

Burning gas in the home
 at 93% efficiency is more carbon efficient than burning fossil fuel at certain power stations. In addition to incurring 6% electricity network transmission losses, these sources of power return relatively poor efficiency:

  • Coal: 34% efficient, 937 gCO2e/kWh
  • Gas Peaking OCGT: 28% efficient, 651 gCO2e/kWh
  • Gas CCGT: 48% efficient, 394 gCO2e/kWh


Hybrid heating and demand side response

As the UK replaces its traditional, centralised power stations with distributed renewables on the grid, the lack of flexibility inherent in renewable sources of power leads to increasing difficulty in balancing supply and demand.

Demand side response (DSR) – the ability to turn down or turn off electrical loads in response to a request from the National Grid – is an established approach to grid balancing in industrial and commercial contexts. DSR provides a valuable source of flexibility back to the grid.

The interim results from the Freedom Project trials show that smart switching between the gas and electric load can be effective in delivering flexible DSR in a domestic setting.

A typical scenario would see the heat pump heat the house using cheap electricity overnight ready for the morning. Come mid-afternoon, the smart controls call on the gas boiler to quickly reheat the property. During early evening, the smart control system can switch between the gas boiler and electric heat pump to avoid adding to peak electricity demands on an overloaded grid.

Hybrid heating systems can move as much demand to gas as they like – they have complete load flexibility. What’s also important is that the ready availability of the gas boiler alternative ensures that reducing demand for electricity never compromises comfort of the occupants.

A significant benefit from hybridised domestic heating is the avoidance of in-home disruption and modification to change over to low temperature heat delivery and deep insulation retrofits.

As well as helping to balance the grid, DSR in a domestic setting enables DNOs to better manage grid constraints and control their investment in network reinforcement as they seek to manage local grid capacity. The Freedom Project is utilising existing electricity network infrastructure capacity and demonstrating wholesale DNO reinforcement can be avoided.


Smart control is key to success

Early modelling has highlighted that conventional approaches to controlling hybrid systems with a simple transition between fuels based on external temperature are likely to perform poorly compared to a fully optimised system.

Control systems should
focus on the heating water temperature, which closely determines efficiency. The smart control panel, developed by Passiv, enables switching between the two heat sources to automatically use the most cost-effective heating mode at any time of the day or night.

The control unit incorporates predictive demand control (PDC) technology, which learns the thermal characteristics of the property to create a physics model of the house and heating system.

PDC chooses exactly the right approach to keep the heat pump running gently while ramping up slowly throughout the night using a dynamically controlled flow temperature. This allows the house to cool slightly, reducing thermal losses, while keeping the heat pump running at a temperature that is as low as possible.

PDC automatically tunes the algorithm to the properties of the house. So, for example, the system would choose continuous heating for a slow responding system such as underfloor heating, or turn off for some
of the night if the house appears to lose heat quickly.

The emerging control strategy for a hybrid heating system is to utilise the boiler to provide bursts of heat to warm the house up quickly, with the heat pump providing temperature maintenance and a ‘base load’ during periods where a fully warm house is not required.


Future plans

The Freedom Project has completed 18 months of a 27-month project programme. Having successfully completed the installations in the summer and early autumn of 2017, the focus has been on optimising the control, monitoring and consumer feedback throughout the current heating season. Once this heating season has concluded we will review and analyse the data and deliver a final report in October 2018. The project has already delivered significant learnings.

With electric-only options presenting higher carbon heat than hybrids, gas boilers, or other gas heating appliances, are not part of a transitionary solution, but are going to be around for the long term. This hybrid approach has the potential to make the best use of the hot water delivery systems currently installed in most UK housing stock. Using gas boilers alongside ASHPs, with some intelligent switching between the two, gives us a pragmatic pathway to decarbonising heat. With the growth of decarbonised gas connections to the gas grid and the significant potential to exploit further opportunities going forward, hybrids could be balancing two renewable vectors to deliver full domestic heat decarbonisation.


Freedom Project partners

Passiv is leading the day-to-day project management, development of control algorithms, designing the architecture of the smart switching system and has overseen the recruitment of homes and the procurement and installation of the hybrid heating systems. The project’s principal funders are Western Power Distribution, the electricity distribution network operator and Wales & West Utilities, the gas distribution network operator.