CPD Programme
Heating capacity in [kW] Water outlet temperature in [°C] Heating capacity in [kW] Water outlet temperature in [°C]
20 20
35 35
18
Conditions:
18
50
Conditions:
50
Heating water flow rate Heating water flow rate
16 16
1.0 m
3
/h 1.0 m
3
/h
14 14
12 12
10 10
8 8
6 6
4 4
2 2
0 0
-20 -10 0 10 20 30 40 -20 -10 0 10 20 30 40
Air inlet Air inlet
temperature in [°C] temperature in [°C]
Figure 2 Selection procedure, step 1 Figure 3 Selection procedure, step 2
> design and selection, plus developments in incorporation of renewables brings other ambient temperature. The type of heat
compressors and controls. benefits. For example, a recent installation at emitter is decided (radiators, underfloor
Heat pumps are most typically applied for a Travelodge used three 28kW air source heat heating, fan coil, etc.), which determines
space heating, space cooling and also for the pumps to pre-heat domestic hot water for the the water temperature required. Underfloor
production of stored sanitary hot water. hotel, helping it to achieve the percentage of heating and fan coils can operate at water
For heating operation, heat pumps will renewable energy required to meet the Merton temperatures of 35C, but radiators will need
always optimise their efficiency at low Rule, as well as achieving compliance with water at least at to 55C.
water temperatures and are most effectively Building Regulations Part L. If a heat pump system is retrofitted into
installed in conjunction with low temperature an existing building that had a gas/oil boiler
heat distribution systems, typically underfloor Defrosting system, the following factors have to be
heating or fan convectors. If conventional Specifiers must also consider the energy impact considered:-
radiators are used, these need to be suitably of an air source heat pump’s requirement • The correct actual flow and return water
oversized in order to allow effective operation to defrost its evaporator to remove ice build temperatures have to be determined for each
at lower water flow temperatures. Radiator up at low ambient temperatures. This is heat emitter (most likely to be a radiator) at
manufacturers provide tables to calculate the most commonly achieved by the heat pump design conditions.
radiator output across a range of mean water switching into reverse cycle operation. When • If the flow temperature required is less than
flow temperatures. this happens the outdoor heat exchanger 55C for all emitters, no additional measures
In the case of underfloor heating, designers (evaporator) becomes the condenser, with are needed for the refit.
should ensure that the underfloor pipe matrix hot refrigerant used to remove the ice. When • If the flow temperature is higher than
is designed with low temperature operation operating in this mode, electricity continues to 55C in some of the emitters, those emitters
in mind (ideally 35C – 40C); this is largely a be used by the compressor and heat is removed must be replaced by larger surface heat
function simply of pipe spacing. from the heat sink (that is the condenser exchangers.
A widely held misconception about heat temporarily becomes the evaporator). This is a • If the flow temperature is greater than
pumps is that they are only suitable for space fundamental reason why air source heat pumps 65C for all emitters and it is not possible
heating and even then, only at low water should always be installed in conjunction or not desired to carry out replacement, a
temperatures. However, heat pumps also with a buffer tank as this prevents heat being high temperature heat pump will need to be
have the ability to provide plentiful hot water, extracted from the buildings heating system used.
either as the sole water heating appliance or, when operating in the defrost cycle. Benefits will be made if the heating
if preferred, in conjunction with another heat Typically the defrosting cycle takes capacity can be reduced by ensuring that air
source such as solar or a fossil fuelled boiler. place between ambient temperatures of infiltration losses are reduced, insulation
As hot water flow temperatures increase, approximately 10C and 0C. In the UK to the building is improved and glazing is
heat pump efficiency (Coefficient of maritime climate where these reflect typical upgraded, all of this in line with the latest
Performance) does drop, but even at a relatively winter temperatures, it is therefore crucial Building Regulations. The result of this is not
low COP
h
of 2, this is still equivalent in terms that the efficiency of the defrost cycle is taken only to reduce the heating requirement, but
of CO
2
emissions to a gas powered system. into consideration and that manufacturers also to lower the water temperature needed
A well-designed and sized heat pump will quoted performance includes energy for heating.
normally be operating above this value, even consumption of the defrost cycle. Accurate selection of an air source heat
for hot water production. New generations pump (ASHP) to meet the demand at a range
of air source technology available from some Selecting a heat pump of outdoor air temperatures is absolutely vital.
manufacturers now offer performance that is For a new build the situation is Remember that ASHP output is a function
comparable to ground source, with high COPs straightforward. The design heating load is of heat source temperature and water flow
at low ambient temperatures. In addition, the determined for a particular winter design temperature, so both efficiency and kW
64 CIBSE Journal February 2010 www.cibsejournal.com
CIBSEfeb10 pp63-66 cpd.indd 64 1/28/10 5:26:19 PM
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76