Verdoppelung der Arbeitszahl von Wärmepumpen und ...

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Verdoppelung der Arbeitszahl von Wärmepumpen und Kältemaschinen mit kleinem Temperaturhub
Author und Coauthors Dr. Beat Kegel, Dr. Beat Wellig, Heinz Richter
Institute or Company Ernst Basler + Partner AG
Address Mühlebachstrasse 11, 8032 Zürich
Telephon, E-mail, Internet-address +41 (0)1 395 16 16
beat.kegel@ebp.ch
www.ebp.ch
Duration of the project 1. Mai 2004 – 1. Nov. 2005
ABSTRACT
DOUBLING OF THE COEFFICIENT OF PERFORMANCE OF HEATPUMPS AND REFRIGERATION
SYSTEMS WITH SMALL TEMPERATURE GRADIENT
The coefficient of performance (COP) of heat pumps and refrigeration systems is closely related to the temperature
difference between the heat source and heat sink. In many applications in building services engineering,
a temperature lift of 10–20 K is sufficient in principle. However, the potential for systems with very
high COP is not fully exploited as standard plants are designed for lifts of 30–60 K. Basic decisions, which
ultimately lead to such a less than ideal design, are taken at an early stage of a project. The main objective
is to give guidelines and rules for the design of systems with small temperature lifts. In a fist step, a refrigeration
system in an office building was analyzed. In this system, the COP increases with decreasing temperature
lift from approximately 4.0 at 25 K up to values around 5.5 at 10 K. If the auxiliary energy consumption
of the fan and pumps is taken into account, the COP is around 3.5 and independent of the temperature
lift. The following measures have to be taken in order to significantly improve the efficiency: (1) The temperature
lift should be kept as small as possible, i.e. neither the evaporation nor the condensation temperature
should be controlled to a constant value. The evaporation temperature should be controlled depending
on the enthalpy of the ambient air. (2) The chiller should primarily run during the night and morning when
the temperature lift is small (at the utmost dehumidification in the afternoon). The stored cooling energy in
the building material can be utilized to offset heat gains during the day. (3) The hydraulic system has to be
very carefully designed. Implementing these simple measures will considerably reduce energy consumption
and on-going operating costs.