gledhill STAINLESSLITE PLUS, Instruction Manual

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