A SHORT CRITIQUE OF SANTON PROPOSALS ON ‘SUSTAINABILITY
(This has been written by Stewart Boyle, Senior Associate at South East Wood Fuels (SEWF) and has received input from OVESCO, SEWF and Southern Solar. It is put forward as a discussion paper for those interested in the NSQ development)
The following is a short critique of the energy-related aspects of the sustainability’ proposals by Santon in their planning application for the North Street Quarter (NSQ) development. It is not offered as a detailed analysis, as hard data in many instances is not available from the Santon paper.
While the Santon ‘Sustainability’ proposal and document – based around work produced by a Maidstone-based consultancy called ‘Daedelus Environmental’ – covers a range of issues, I have concentrated solely on the critical energy equation on site. I look briefly at the proposals for the energy efficiency of the buildings and the proposed energy use for heating, cooling, hot water and power on site. I have not dealt with water, waste management or transport issues on site which others have reviewed.
Summary of Santon Proposals
Energy efficiency levels in buildings are in advance of Building Regulations – ranging from 33%-50% improvements (measured in terms of watts/m² heat loss) (see Para 2.2.9)
Some acknowledgement is given to the benefits of solar orientation in the buildings to capture potential benefits for ‘passive solar’ design, solar thermal heating, and solar PV on roofing for electricity (2.2.1-2.2.5), but no data is provided on what these benefits could be
Four options are considered for space and water heating and (some non-domestic cooling) on site (para 2.2.15-2.2.19):
Big gas boilers and gas-fired CHP to deliver space and water heating via a district heating network
As above but only for the higher density part of the development, with gas condensing boilers for the remaining homes
A water-based heat pump system using the River Ouse as a pre-heat source. This is described as an ‘open loop river extraction’ system.
Standard gas condensing boilers for all buildings optional 1-1.5kW(e) solar PV roof arrays for home purchasers (para 2.2.20)
Issues and Concerns over the Proposals
Fundamentally, the existing Santon proposals could well be a major missed opportunity for low carbon energy in Lewes. Such a missed opportunity would have significant long-term negative implications during the lifetime of the buildings. At a time when concerns over climate change are growing and the UK is on course at national level for a 80% plus reduction in carbon emissions, the Santon proposals are dressed up as ‘low carbon’ but in truth are somewhat vague, lacking in substance and with big gaps in critical data. Specifically, we comment on the proposals as follows:
- The energy efficiency proposals are a good step towards low-zero carbon status for the development. While they are an improvement on Building Regulations minimum efficiency standards, they are by no means close to ‘Zero Carbon’ homes standards (para 2.2.23).
- Unless zero-low carbon options are adopted for the residual heating and power needs, then the site will still be a significant producer of carbon emissions (see below). While there is discussion of the possible benefits of ‘passive solar’ gains through building orientation and other measures, no quantification is given for this in terms of annual carbon reduction benefits or in reducing residual heating needs and costs. This is remiss and it means that the developers cannot claim ‘passive solar’ benefits. It is arguable whether the proposed layout of the plan would allow such passive solar gains to be obtained. It seems a mere flag waving exercise of the supposed benefits.
- By opting for standard domestic or big boiler gas heating, and gas CHP for 3 out of the 4 options considered by Santon consultants, in effect they considered only a single true lower- carbon technology – the river-source heat pump system. Even this is not a true low-zero-carbon option unless the electrical consumption component is low-zero carbon (see below).
- Gas is a ‘grey-green’ fuel at best, and should not even have been considered as a main source of heating if low carbon development is the goal. Gas-fired CHP provides only 10-15% carbon improvements at best over standard brown power from the grid plus a gas condensing boiler solution. CHP systems have to be run very well to ensure even these limited benefits.
- Other low-carbon heating options such as modern wood heating (biomass), or solar thermal heating for hot water were not considered in the analysis. This seems an omission as both are well established technologies with very low CO2 emissions factors (see Figure below).
- Modern wood heating is now commercially viable across the UK with more than 20,000 projects (domestic and commercial) supported under the Government’s Renewable Heat Incentive (RHI).
- Santon have opted for a relatively new and in some ways more risky low-carbon heating source, namely river water-based heat pumps. While ground-source (GSHP) and air source heat pumps (ASHP) are quite familiar technologies in the UK, and are commercial and useful in the right setting, water-based (river) systems have very few systems in operation.Data is hence very limited and relative costs are apparently high. By opting for this technology, plus opting for an ‘Open Loop’ system, they are proposing a system which has higher risks than other low-carbon technologies. An ‘open loop’ system in a tidal river has potential salinity issues – a problem Santon admit. Though it can be managed with appropriate technology and materials choices, detail on how it will be managed is currently missing. It will also face negotiations with the Environment Agency over gaining ‘abstraction licences’. ‘Closed loop’ systems, while offering slightly lower conversion efficiencies, would obviate the salinity-corrosion problem and not require abstraction licences.
- There is very limited information given on the heat pump technology proposed, and its related costs and benefits. Reference is made to an HNDU (DECC) funded project where this has been assessed (paras 2.2.17-2.2.18), but despite 15 months of effort the report is not being promised until AFTER the planning window for objections. No hard technical and performance data, costs data, or a review of technological risks are provided. Hence no sensible evaluation of this proposal can be carried out by others. This gives some cause for concern that the energy proposals may be a PR exercise by the developer and not a properly evaluated engineering proposal with clear and firm carbon saving benefits demonstrated.
- Heat pumps require significant levels of additional power usage to upgrade low temperature heat from a river (quoted at 9oC in the proposal) to usable temperatures of >30-35oC in a building (higher temperatures for hot water). The overall coefficient of performance (COP) of a heat pump, including distribution, should be at least 3 (personal communication, Nick Rouse, OVESCO). The existing figure for centrally generated electricity is c.500gCO2/kWh)1.
- This means that a heat pump system is producing heat at c.166gCO2/kWh. This would be lower if a COP greater than 3 can be obtained, and lower again as central electricity generation is slowly decarbonised due to the impact of renewables.
- A district heating (DH) network system uses big pumps for the circulation of water through the underground pipework network. Movement of water through the ‘Open Loop’ river heat extraction system will also require big pumps. Overall, such increases in on-site power consumption, relative to a standard ‘boiler in every house’ option, will create additional CO2 emissions.Unless the power consumption is supplied directly or ‘netted out’ by low-carbon power solutions such as solar PV or wind power for example, there will be a net increase compared to either gas condensing boilers or a biomass based district heating network. No reference is made by Santon to either this issue or any proposed solutions.
- Gas heating produces an estimated 212g CO2/kWh and possibly 10-15% higher for district heating systems as there are losses in the distribution system. For gas-fired CHP systems – i.e. producing both heat and power on-site at an average efficiency of 80% – the estimated CO2 savings are rated as a “minimum 10% CO2 savings for good quality natural gas CHP in comparison to conventional forms of energy generation”2. Based on data produced by the BRE for DECC (Ref 1), the following are carbon emissions factors in grams of CO2 per kWh of energy (gCO2/kWh) for various heating and power options. This with ‘S’ in title are currently included as Santon energy options. Others included in this chart are not currently included.