Existing measures, with projected energy savings made
Photovoltaic (PV) or solar generation Solar water heating
Installation of variable speed drives on selected pumps
Lighting level review and reduction
Staff engagement – estimated outcome Totals
Electricity savings estimate (kWh/yr)
10,000 2,900 1,000 11,800
4,500 27,300
10,000 12,900
estimate (kWh/yr)
savings
Gas
(te CO2/yr)
5 1
1
Carbon dioxide saving
saving (£/yr)
1,000 80
100
Cost
Guide price (£)
27,500 5,000
250
6 1,060 3,500 4
17
3,600 5,840
Simple payback
period (yrs)
27.5 62.5
2.5
1,000 37,250
Figure 1: Measures in operation, with projected energy savings made, projected payback periods and expected savings to be made
Recommended further measures, with estimated energy and cost savings
Installation of ground source heat pump
Voltage optimisation
electricity savings (kWh/yr)
Guide
electricity savings (kWh/yr)
–33,000 176,000 9,000 Gas
Carbon dioxide savings
(te CO2/yr)
saving (£/yr)
Cost
Guide price (£)
Simple payback period (yrs)
14.8 1,900 50,000 26 4.8 900 9,000
Figure 2: Recommended further initiatives. The figures shown are estimates of what savings could be made through the adoption of these measures
Metered energy Actual
Electricity kWh/sq m Non-electricity kWh/sq m
Carbon kg CO2 emissions/sq m Building total Kg CO2 Building total cost (£)
75
184 74
180,511 31,626
Benchmarks
Adjusted Good practice 79
184 76
185,729 32,597
55
385 101
244,746 41,414
Typical 80
540 143
347,007 58,782
Figure 3: Comparison of electricity use and carbon emissions with benchmarks >
an energy management consultancy, to conduct an assessment of the impact of these improvement measures on the energy efficiency and carbon footprint of the Wembley site. The commission was the result of CIBSE’s ongoing programme of investigations into real-life building performance. The detailed analyses of the overall energy use and performance of heating, ventilation and other systems were undertaken using the CIBSE TM22 procedure. The energy saving measures taken as a result of the refurbishment have been shown to have produced substantial projected savings – see Figure 1, above. These measures were the installation of photovoltaics and solar-powered water heating. In addition, a staff- engagement programme was introduced to help improve energy management, which produced notable estimated savings. Together, these three changes have produced
assessed annual cost savings of nearly £6,000, within a range of identifiable payback periods (Figure 1). Power Efficiency also recommended a range of further
energy saving measures that could be undertaken at the site. These were the installation of a ground-source heat pump and the application of voltage optimisation. Projected savings are shown in Figure 2. Below, we look in more detail at the impact of the
36 CIBSE Journal February 2011 10
3.3 0.3
refurbishment measures taken at the site. We also explain our recommendations for further improvement. But first, let’s look at the metering arrangements.
Energy consumption Metering arrangements at the site comprise one non- half-hourly meter for imported electricity and one meter for gas used on site. In addition there are four non-half-hourly sub-meters dedicated to metering the Life Building, the main boiler plant and appliance bay space heaters, and associated gas consumption. A single non-half-hour meter logs the imported consumption from the PV installation. Fiscal metering data is uploaded to the supplier’s web portal and can be interrogated remotely by the LFB. Energy generated on site by the PV system has
reduced the amount of imported electricity. Electrical energy generated by the PV system since installation in 2008 was, at the time of the study, 20,900 kWh, therefore averaging in the order of 10,000 kWh per year, representing a contribution to the electrical income of 6.2%. The total electricity consumption for 2008 was
194,728 kWh plus the estimated 10,000 kWh, which resulted in a combined total of 204,728 kWh, whereas the total electricity consumption for 2009 was 180,968 kWh plus the estimated 10,000 kWh, thereby resulting in a combined total of 190,968 kWh. The above totals indicate an overall reduction in the sites’ total electrical consumption of 13,760 kWh (6.7%). Gas is consumed on site by five gas-fired boilers, two
space heaters, and the kitchen appliances. The total gas consumption for 2008 was 477,182 kWh. In 2009 it dropped to 446,067 kWh, a fall of 6.5%. A comparison of the metered energy use at the site
with ‘Good Practice’ and ‘Typical’ benchmarks is shown left (Figure 3).
Existing improvements Photovoltaics: The fire station has a photovoltaic (PV) system which generates 11.3 kW of renewable electricity, and has a predicted average annual output of 10,000kWh. This represents an annual emissions saving of 5 tonnes and an annual cost saving of £1,000, increasing to nearly £5,000 with the benefit of electricity feed-in tariffs. These figures are based on an electricity charge of 10p per kWh. Half the cost of the system was covered by an Energy
Efficiency Loan, leaving the LFB with a bill of £27,500. This produces a payback period of 27.5 years, but this timescale has been reduced considerably as a result of the introduction of feed-in tariffs in April 2010. Solar heating: The site has a solar-powered water-
heating system, using evacuated tube collectors covering an area of 5 sq m on the roof of the Life Building. The system has not been monitored, but it is capable of cutting annual gas consumption by 2,900 kWh, saving an estimated £80 a year. This would also reduce CO2 emissions by 0.5 tonnes a year. With these cost savings, the payback period for the system is estimated at 36
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