Bath Western Riverside Energy Centre provides the heating and hot water via a district heating system to approximately 800 homes on the newly built Crest Nicolson development at Bath Western Riverside.
For those of you who didn’t get the opportunity of visiting the centre during Bath Green Homes we felt it would be useful for us to write-up our experience of visiting the centre and in particular a technical description.
When plans for Bath Western Riverside were drawn up Crest Nicolson agreed with B&NES council to build the homes to Code for Sustainable Homes (CfSH) level 4. This imposed a higher than minimum Building Standards level of sustainability on the development. Developers have some flexibility in how they implement this, generally and most cost effectively by installing solar PV panels to lower CO2 emissions.
Following discussions with B&NES Crest Nicolson decided against solar PV panels because their aesthetics would be difficult on this sensitive city centre site and because of the tall buildings there is relatively little roof area for per storey. They therefore selected an alternative of a biomass and CHP district heating which would allow them to meet CfSH 4. The split of the onsite overall 31% carbon savings required to meet CfSH 4 over minimum building regulations (2006 Part L?) is: 25% biomass, 50% CHP, 25% building fabric
The most effective way of implementing this choice was to build a single ‘energy centre’ containing the boilers and then distribute the heating via a district heating network to the homes on the site. The Energy Centre has been built and run by EON under contract from Crest Nicolson.
The Energy Centre contains 3 different heating systems:
- A biomass boiler
- A gas CHP (Combined Heat and Power) boiler
- 2 x gas boilers
Depending on demand some or all of these boilers are used to heat a 30m3 thermal store. This thermal store then circulates hot water via a circulatory insulated pipe network (district heating network) to 800 homes on the site. Each home has a heat exchanger which takes heat from the heating network when demanded by the home’s heating or hot water system. The heat exchanger unit has a thermal meter built into it which is used for charging EON’s customers. The whole system is controlled and monitored remotely from Brighton.
The biomass boiler uses wood pellets to produce heat.
- About every 2 weeks during the winter a lorry delivers pellets to the site which are fed into a large store next to the boiler, and an auger automatically takes the pellets from the store and transports them to the boiler for combustion
- EON decided to use wood pellets, despite being 60% more expensive than wood chips because of poor experiences on previous developments with the quality of woodchips and problems maintaining the boilers as a result
- Using wood provides a low carbon source of energy as CO2 is absorbed during the growth phase of the trees which is then released when burnt; so almost no net carbon is emitted over the full life cycle of this process. In addition the pellets are a waste by-product of the timber industry (typically saw dust) which might not otherwise have a use
- The capacity of the boiler is about 400kW and is 80% efficient, and is designed to top up the heating from the gas CHP system during the winter heating system
More information is available from this poster.
Gas CHP System
The gas CHP (Combined Heat and Power) is used to provide most of the hot water for the site.
- The ‘boiler’ consists of an internal combustion engine (truck engine) power by natural gas. The mechanical energy from the engine drives a generator which provides electricity. Any spare heat is then distributed to the homes (via the thermal store)
- CHP is an efficient way of generating low carbon electricity where it displaces fossil fuel power stations on our national grid. Even the most efficient traditional gas turbine is only 50% efficient; the 50% of the remaining energy is permanently lost as heat. In a CHP system by distributing the heat the system can be up to 90% efficient, almost halving the CO2 produced compared with a traditional gas turbine system
- The CHP system is the main provider of energy for the site and has an output capacity of 230 kW of electricity combined with 350 kW of heat
More information is available on this poster.
As a backup to the base-load heat provided by the biomass and CHP boilers there are 2 large capacity 2.3MW gas boilers which are only designed to work for a few hours per year during peak loads. More information is available on this poster.
To deal with peak loads in the system, typically during the morning when everyone is showering there is a 30 m3 thermal store. It has enough capacity to supply 2000 showers for 5 minutes. More information is available on this poster.
Other background information
- The major benefit of a district heating system is that it future proofs the heating on the site, so for example when new lower emissions technology comes along in future only one boiler needs to be replaced rather than 800 individual gas boilers in the homes
- The largest downside of such a network is about 25% of the heat is lost in the network via the insulated pipes and riser pipes within the buildings
- EON guarantees to charge residents less that the equivalent home would have to pay with a gas boiler. They is however a flat £300 standing maintenance charge, which although it sounds expensive means the residents a. avoid boiler service costs (£100 per year?) and b. boiler replacement costs (£2000 every 15 years?). Curo absorb some of this standing charge for their social housing residents
- A couple of residents of Riverside joined our tour, in general they were happy with the system, apart from problems with getting hot water to top floor flats (something Crest Nicolson said they would look into), and overheating in the summer which we presume is because there is no provision for external shading in the properties?
- Going forward the energy centre doesn’t have the capacity to generate heat for the remaining 1200 homes on the site, including those properties on the other side of the River Avon. Although a decision hasn’t been made Crest Nicolson are considering small gas boilers distributed around the remainder of the site. To offset the higher carbon of these conventional boilers they are considering improved fabric (better insulation), the fabric is relatively good and includes 1.2 w/m2/k U value double glazing