Hulley Eco Long Term Energy Strategy
Hulley Eco is often involved in masterplan developments consisting of mixed use commercial, retail and residential units. These developments are often phased, and can take a decade or more to make it from Stage 1 Preparation & Brief through to completion.
The introduction of minimum energy standards through building regulation has not only changed how we think about design, it has changed how developments are funded and marketed. Funders and developers both are more frequently demanding EPC A rated buildings and often require that BREEAM Excellent certification is achieved. We are inevitably required to deliver a sustainable, low energy and low carbon energy strategy.
In parallel we have seen the push from central government and local authorities to consider centralised community / district heating as a priority in order to reduce carbon emissions associated with heating demand.
In England the London Plan (known for the catchphrase Lean, Clean and Green) champions low energy design, local energy generation and the creation of, or connection to, local district heating. This approach has fed into local authority planning guidance throughout England. Many cities are aiming to push developments away from building localised plant by developing heat network infrastructure.
North of the border, the Scottish Government has a long-term target to reduce greenhouse gas emissions by 42% by 2020. In fact this has recently been increased to more than 50% by 2020. Scottish Government have issued Heat Policy Statement 2015 and followed up with a Consultation on Heat & Energy Efficiency Strategies, and Regulation of District Heating issued January 2017. Schemes such as the Low Carbon Infrastructure Transition Programme (LCITP) have been established to help fund the creation of low carbon district heating energy networks.
In developing a long term masterplan energy strategy, we are pointed in the following direction;
Minimise energy demand (fabric, lighting, services efficiency),
Prioritise community heating with development centralised energy centres to rationalise plant size and optimise efficiency,
Incorporate LZCTs into the heating infrastructure as a lead device.
The initial energy concept design is often carried out relative to building regulations current at the time, and the inclusion of LZCTs within the central plant mix is justified on the CO2 emission reduction that would be achieved if the system were live at the date of analysis.
At present CHP is the tried and tested solution that reduces CO2 emissions, reduces the primary energy factor for the development and provides a quick payback on a comparatively low upfront capital expenditure.
It is important however to consider how the environmental performance of a system will fluctuate relative to the timescales of a development.
Will a CHP lead district heating energy strategy still deliver low carbon energy in 5 years’ or 10 years’ time?
The increasing contribution of renewable technology such as on-shore / off-shore wind turbines is reducing the carbon intensity of the national grid. The carbon emission factors for both Grid Supplied and Grid Displaced electricity are forecast to reduce over the next 15 years, dropping to half of the current intensity by the 2030s.
As grid carbon emission factors reduce the effectiveness of on-site low carbon equipment changes as a result. Energy strategies and their CO2 emission reduction credentials hinge on the official carbon emission factors for Natural Gas, Grid Supplied Electricity and Grid Displaced Electricity.
In the coming years CHP lead district heating strategies will become more carbon intensive as the CO2 emission factor for gas remains constant whilst the benefit of grid displaced electricity reduces.
There will come a point where the intensity of grid displaced electricity is too low to compensate for the carbon emissions associated with gas consumption. At this point CHP will be more carbon intensive than gas fired boilers.
High efficiency gas fired boilers could outperform CHP in 5 to 10 years’ time.
The reduction in grid supplied electricity factor directs us toward electric heat pump strategies. The performance of electric heat pump district heating strategies will improve over time as the carbon emission factor for grid supplied electricity reduces. Less emphasis will be placed on system SCoP from a CO2 perspective, allowing systems that generate higher temperature LTHW to be used within traditional LTHW systems.
However, with current carbon emission factors, strategies that incorporate electric heat pumps as a lead device require the use of lower district heating flow and return temperatures to achieve a high SCoP and comply with building regulations. This complicates the supply of heat at a high enough temperature to generate domestic hot water to connected buildings.
We find that a hybrid system incorporating both gas fired CHP and electric heat pumps is the optimum solution.
Heat pumps can be incorporated to preheat district heating return water, operating in a temperature range that optimises system SCoP. CHP plant can then lift the supply temperature allowing the use of traditional LTHW emitters and allowing domestic hot water to be supplied via heat interface units to connected residential units. CHP power generated can ideally be aligned to match the power demands of the electric heat pump units.
This combination appears to offer the benefits of low CO2 emissions today, whilst providing a comparatively stable low carbon solution moving forward. It also provides the opportunities for the lowering the cost of energy to generate heat which could help combat fuel poverty.
Hulley Eco has considered this exemplar low carbon district heating strategy for the EDI India Quay project in Edinburgh, a phased mixed use residential and commercial development. This will serve as a case study for similar H&K projects throughout the UK over the coming years.