CPD Programme
Heating capacity in [kW] Water outlet temperature in [°C]
20 Lifetime ownership cost and CO2 emissions comparison
35
18
Conditions:
CO2 emissions kg (000’s) 10 20 30 40 50 60 70 80
50
Heating water flow rate
16 CO2 emissions (kg)
1.0 m
3
/h
CO2 emission
Capital & installation cost
14
Air source heat pump Costs (£)
Heating distribution system
Fuel costs
12 CO2 emissions (kg)
Servicing maintenance
Ground
pump
10
source heat
Costs (£) 10 year replacement cost
8
CO2 emissions (kg)
LPG
ondensing Costs (£)
6
C
4
CO2 emissions (kg)
ondensing Costs (£)
2
C
Oil Boiler
0
CO2 emissions (kg)
-20 -10 0 10 20 30 40
ondensing Costs (£)
C
Gas Boiler
Air inlet
temperature in [°C]
Costs £ (000’s) 5 10 15 20 25 30 35 40
Figure 4 Selection procedure, step 3 Figure 5 CO2 Emissions and lifetime costs for various fuels
rating will decrease at colder times of the year. source to reach the maximum temperature – 30C, which is circulated directly through the
The capacity of the heat pump needs to be this might be from another heat source, such system and used to provide hot water at 60C
matched to the energy demand during cold as a fossil fuel boiler, or from a boost electric for the staff canteen and washrooms, and
periods. The following example illustrates the immersion heater. customer toilets.
factors that need to be considered. Figure 2 Correct selection of the hot water cylinder In the current economic climate, many
shows the heating demand as 11 kW with the with an appropriately sized heat exchanger businesses will find the costs of a new
red line, the room design temperature is 21C to ensure maximum heat transfer is renewable heating system off-putting. But
and the ambient air design temperature is -3C important as heat pump systems usually building managers should bear in mind that
(green). The diagonal purple line intersects the require a larger heat exchanger surface the Renewable Heat Incentive(RHI) comes
heat pump output curve to give the bivalent into effect in 2011, which will provide a direct
or balance point (1C ambient). From Figure 3, financial return for every kWh of renewable
the heat pump contributes 100 per cent of the
In the current
heat generated. And to minimise the impact of
heating demand at this balance point.
economic climate, many
the initial capital costs of installation, leasing
When the ambient temperature falls schemes can cover the complete project outlay
below the balance point, Figure 4 shows how
businesses will find the
and spread the costs over up to 15 years.
the heat demand increases, while the heat
costs of a new renewable
Repayments can very often be met by the
pump output falls, such that about 3 kW of
heating system
savings made on fuel bills, and payments from
supplementary heating has to be provided. the RHI will also make a useful contribution.
Other factors that may affect the heat pump
off-putting
Figure 5 measures total lifetime costs
output are: against different fuels and also total CO
2
• Wind speed affecting fan on outdoor unit area. This is particularly important for air emissions (electricity based on 0.422kgCO
2
/
• Positioning in relation to the building (dead source heat pumps to ensure that stored hot kWh) for a three-bedroomed new-build
areas) water temperatures can be maximised in semi-detached house over a 20-year
• Orientation and shading the summer months when the heat pump period. Heat pumps are a viable option in
• Geographical height and area output will increase due to higher ambient commercial buildings, for hot water as well
• Defrost requirements air temperatures. Cylinder specification for as space heating, offering great flexibility
air source heat pumps therefore needs to be over installation and system design. It is a
Hot water storage carefully considered in line with performance question of specifying the right heat pump
The ability to provide sufficiently high water characteristics of the heat pump. for the specific task in mind, and siting it to
temperatures for stored hot water is also Commercial cylinders compatible with gain the optimum performance.
important, both from an efficiency point heat pumps are available in sizes up to 4,000 © Terry Welch
of view and also to meet Health and Safety litres, with coil size bespoke designed to
legislation aimed at preventing legionella. For exact specification. Hybrid systems of solar References
heat pumps specified primarily for hot water thermal and heat pumps are also possible and Heat Pump Benefits: http://www.dimplex.
production, high temperature models are able becoming increasingly popular. Intelligent
co.uk/products/renewable_solutions/heat_
to achieve stored hot water temperatures of up heat pump controls can optimise use of the pump_Benefits.htm
to 65C without the need for supplementary solar energy before bringing on the heat pump The CIBSE Journal CPD Programme: May
heating. These typically use refrigerants such compressor. The use of waste heat is also an 2009, Heat Pump Technology
as R290 (Propane) or R134a to achieve higher interesting application for heat pumps. Heat Heat Pump Design, http://www.dimplex.
temperatures within the vapour compression pumps installed at the first supermarket in de/en/downloads/planning-manuals/
cycle. Lower temperature heat pumps will Ireland built to Passivhaus standards use the heat-pumps/heat-pumps-project-planning-
require support from a supplementary heat waste heat from the chiller cabinets at around manual.html
www.cibsejournal.com February 2010 CIBSE Journal 65
CIBSEfeb10 pp63-66 cpd.indd 65 1/28/10 5:26:54 PM
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