gledhill 120IND, Design, Installation & Servicing Instructions

Page: 7 / 20

Page 7
DESIGN
TECHNICAL DATA
Sizing the Buffer store to the Heat pump
Buffer stores should be sized as per the table below (source paragraph
4.5 BS EN 15450).
One heat pump manufacturer recommends that -
‘… A prerequisite for energy-efficient operation is the proper design of
the heat source system and the heat utilization system. One of the most
important factors of heat pump efficiency is keeping the temperature
difference between the heating water and the heat source as small as
possible. It is therefore strongly recommended that the design of both
the heat source system and the heat distribution system be carried out
with great care.
A 1 Kelvin (1C) higher temperature difference corresponds to an increase
in power consumption of approximately 2.5%. When designing the heating
system care must be taken that special applications such as domestic water
heating are taken into consideration and dimensioned for low temperature
operation. Heat pumps are optimally suited for underfloor heating (surface/
radiant heating) applications due to the low supply temperatures (30˚C to
40˚C). A considerable contribution to the economical operation is made
by the heat pump controller provided it is set correctly…’
Using the buffer store in conjunction with an additional heat source
requires a more sophisticated control system. This is to stop the boiler
dominating the heating of the cylinder and reducing the possible input
of the heat pump.
Several alternative arrangements are shown on page 7 & 8. It is also
possible to use a buffer vessel in a serial arrangement, either in the return
or flow from the heat pump.
Heat Pump Sizing
Cylinder capacity Heat pump output
90 litres 2.6kW - 7.5kW
120 litres 3.4kW - 10kW
210 litres 6kW - 17.5kW
300 litres 8.5kW - 25kW
400 litres 11.4kW - 33.3kW