Technical data

www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 95
Integration of the heat pump in the heating system 8.3.2
8.3 Safeguard the heating water flow rate
The minimum heating water flow rate listed in the device informa-
tion must be maintained for all operating states to guarantee the
functional operation of the heat pump. The circulating pump
should be dimensioned so that the water flow through the heat
pump is also maintained even if there is a maximum pressure
drop in the system (almost all heating circuits closed).
The required temperature spread can be determined in two pos-
sible ways:
 Arithmetical calculation
Chapt. 8.3.1 on page 95
 Reading out of tabular values in relation to the heat source
temperature Chapt. 8.3.2 on page 95
A number of different points must be taken into account when de-
fining the heating water flow rate in the heat pump generator cir-
cuit. The minimum heating water flow rate must be guaranteed in
all operating situations. With controlled pumps, it is particularly
important to ensure that the pump is set to a constant speed (e.g.
Grundfos Alpha 2) and that the internal control functions of the
pump do not result in a brief fall in the volume flow (e.g. pump
standstill due to ventilation function during air bubble detection).
With lower flow temperature, a higher volume flow is desirable,
which is dependant on the system and the heat pump used. The
following spreads are recommended in the in the design point:
 35°C: approx. 5 K spread, but never below
minimum heating water flow rate
 45°C: approx. 7 K spread, but never below
minimum heating water flow rate
 55°C: max. 10 K spread, but never below
minimum heating water flow rate
 65°C: max. 10 K spread, but never below
minimum heating water flow rate
On systems with extremely low system temperatures (flow tem-
peratures <
25°C) a max. spread of 5 K must be specified in the
design point during planning. Systems for heating and cooling
must be designed for the highest required water flow (heating
water or cooling water throughput).
8.3.1 Arithmetic calculation of the temperature spread
 Determination of the current heat output of the heat pump
from the heat output curves at the average heat source tem-
perature.
 Calculation of the required temperature spread using the
minimum heating water flow rate listed in the device informa-
tion.
NOTE
Tabular values for the required temperature spread in relation to the heat
source temperature can be found in Chapt. 8.3.2 on page 95.
Example: air-to-water heat pump:
Heat output
HP
= 10.9 kW at A10/W35
Specific heat capacity of water: 1.163 Wh/kg K
Required minimum heating water flow rate:
e.g. V = 1,000 l/h = 1,000 kg/h
Required spread:
8.3.2 Temperature spread in relation to the heat source temperature
The heat output of the heat pump depends on the heat source
temperature. With the heat source external air in particular, the
heat output generated by the heat pump depends heavily on the
current heat source temperature.
The maximum temperature spread in relation to the heat source
temperature can be found in the following tables.
Air-to-water heat pump,
Table 8.1: Outside air heat source (temperature can be read from the heat
pump manager!), operation with 1 compressor
4
Heat source
temperature
Max. temperature spread between
heating flow and return
of to 2 Compressor 1 Compressor
-20 °C -15 °C 2K 4K
-14 °C -10 °C 2.5K 5K
-9 °C -5 °C 3K 6K
-4 °C 0° C 3.5K 7K
1°C 5 °C 4K 8K
6°C 10 °C 4.5K 9K
11 °C 15 °C 5K 10K
16 °C 20 °C 5.5K 11K
21 °C 25 °C 6K 12K
26 °C 30 °C 6.5K 13K
31 °C 35 °C 7K 14K