Case Study 12 - Combined Heat and Power (CHP), District Heating and Energy Strategy
Perthshire Housing Association and Servite Housing Association, Scott Street, Perth
| Type: | New build, solid masonry, 3 and 4 storey flatted | |||
| Number of units: | 33 general needs flats (PHA) plus PHA office accommodation and 30 unit sheltered housing (SHA) | |||
| SAP rating: | n/a and does not allow for district heating or CHP | |||
| U-values: | 0.35 Wm2C roof 0.45 Wm2C walls 0.45 Wm2C floor |
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| Fuel costs: | £6.18 pw (Servite HA) |
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| Works costs: | £3,500,000 total excluding office fit out |
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| Unit cost: | £49,795 (Servite HA) | £40,421 (Perthshire HA) | ||
| Completion date: | April 1999 |
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| Contacts | Client: | Perthshire Housing Association Servite Housing Association |
Alison Cook Andrew Kirkpatrick |
01738 441088 01382 480915 |
| Architect: | Keppie Architects | Geoff Taplin | 01738 631551 | |
| Builder: | Brown Construction | C Jolly | 01382 739683 |
This is a mixed-use development by Perthshire Housing Association (PHA) and Servite Housing Association (SHA). The development comprises 33 flats for PHA plus a 30 unit sheltered housing development in a separate but adjacent building for SHA. The buildings are four storey tenements with new offices for Perthshire Housing Association on the ground floor of the PHA building. The development is on a brownfield site and is very central with local amenities immediately adjacent. Parking is well below planning guidance levels and the development is well served by public transport.
Key Features
Energy Use
CHP, District Heating
The sheltered housing was designed to use district heating on a 24 hour basis and a joint development of this scale and diversity of power demands offered an ideal opportunity to install combined heat and power.
The CHP plant is a modified transit van "lean burn" engine which generates electricity using gas instead of petrol. The heat produced by the generator is recovered to heat water. Water is also heated by the district heating system, which consists of a series of boilers in the plant room. Hot water is pumped around the buildings to heat wet radiators in each room. To the tenant the system looks normal other than not having a boiler in the home. The CHP is deliberately undersized to avoid unnecessary surplus in the summer and produces up to 40% of the electricity required, the remaining power and back up in case of failure coming from mains gas and electricity. The use of CHP increases the efficiency of electrical production from 30% (standard power stations) to 85%.
The CHP installation formed a separate specialist contract outwith the main building contract to accommodate the need for a nominated supplier.
Figure 12.1 Rear view of scheme showing gable end flue to CHP plant room.
Figure 12.2 Front view of the scheme showing mixed use with Perthshire Housing Association offices immediately below the residential accommodation.
Benefits
- less pollution through more efficient heat and power generation (CO2 emissions reduced by 50%)
- lower fuel bills for tenants and the Associations. This is achieved through the CHP and because the Associations can enter into bulk purchase agreements with power suppliers
Perthshire Housing Association are now in negotiation to extend the use of CHP as part of their volume procurement contract for 300 dwellings over 3 years. This will involve partnership with a local hospital, school and housing.
Social and Management
Metering of District Heating, Mixed Use
Running costs for gas and electricity and maintenance costs for the CHP will be recovered from the tenants and PHA office. PHA tenants pay a weekly service charge for heating varied according to size of flat (£3.40 for one bedroom and £4.55 for two bedrooms in 1999). Individual use of hot water and electricity will be metered with each flat fitted with a pre-payment meter. Tenants purchase £5 cards from the office downstairs or from a local shop. Every £5 card buys 100KWhrs of electricity compared to the normal tariff which would buy 56KWhrs. Since PHA is the power supplier it must take responsibility for debt recovery and voids. The use of pre-payment cards minimises the need for management and meter readings.
In Servite.s sheltered properties, the tenants pay all fuel charges along with their monthly rent and therefore benefit from costs being spread evenly over the year. A proportion of the cost is identified for common areas and remaining costs vary according to the size of the flat.
A management agreement has been established to determine the duties and responsibilities of the two Associations. Servite manage the CHP and are responsible for the gas supply in order that the two associations can benefit from Servite's ability to procure gas at approximately 35% savings on normal domestic tariffs.
The location of the Perthshire Housing Association offices within the building provides a mixed use development.
Other Relevant Aspects
Costs and Maintenance
Costs are within an agreed budget with Scottish Homes. The CHP plant cost £45,000 in addition to the district heating boiler, pipework and radiators, offset by £17,000 with a grant from Energy Efficiency Standards of Performance. The meters cost £300 to install. The payback on installing the CHP system in terms of reduced energy bills is 3-5 years. Regular maintenance of the CHP plant is essential and costly.
Perthshire Housing Association are currently considering the transfer of the capital cost of future energy efficiency measures to a revenue cost via leasing agreements. Revenue costs can then be recovered by increasing the rents by a proportion of the savings to the tenant from the energy efficiency measures. Servite passes all savings on to the tenants.