Compression heat pump and chiller¶
Simple calculations for compression heat pumps and chillers.
Scope¶
This module was developed to provide COP calculations based on temperatures for energy system optimizations with oemof.solph.
A time series of precalculated COPs can be used as input for a transformer (an oemof.solph component) in an energy system optimization. Discover more possibilities to use this module with our examples: https://github.com/oemof/oemofthermal/tree/dev/examples
Concept¶
Compression heat pumps and chillers increase the temperature of a flow using a compressor that consumes electric power. The inlet heat flux comes from a low temperature source (T_low) and the outlet has the temperature level of the high temperature sink (T_high). The same cycle can be used for heating (heat pump) or cooling (chiller).
The efficiency of the heat pump cycle process can be described by the Coefficient of Performance (COP). The COP describes the ratio of useful heat ( or ) per electric work consumed:
The Carnot efficiency describes the maximum theoretical efficiency (ideal process). It depends on the temperature difference between source and sink:
for heat pumps and
for chillers.
To determine the COP of a real machine a scaledown factor (the quality grade ) is applied on the Carnot efficiency:
with
Typical values of quality grades are 0.4 for airsource heat pumps, 0.55 for groundsource (“brinetowater”) heat pumps using a ground heat exchanger, and 0.5 for heat pumps using groundwater as source. [1]
For high temperature heat pumps Arpagaus finds quality grades between 0.4 and 0.6. [2]
Fig.2 illustrates how the temperature difference affects the COP and how the choice of the quality grade allows to model different types of heat pumps.
Usage¶
These arguments are input to the functions:
symbol attribute explanation cop
Coefficient of Performance temp_high
Temperature of the high temp. heat reservoir temp_low
Temperature of the low temp. heat reservoir quality_grade
Quality grade temp_threshold_icing
Temperature below which icing occurs factor_icing
COP reduction caused by icing
The Coefficient of Performance (COP) is calculated using `calc_cops()`
COP = calc_cops(temp_high,
temp_low,
quality_grade,
temp_threshold_icing,
factor_icing,
mode)
mode=’heat_pump’
mode=’chiller’
The maximum cooling capacity can be calculated using `calc_max_Q_dot_chill()`.
Q_dot_chill_max = calc_max_Q_dot_chill(nominal_conditions, cops)
The maximum heating capacity can be calculated using `calc_max_Q_dot_heat()`
Q_dot_heat_max = calc_max_Q_dot_heat(nominal_conditions, cops)
The quality grade at nominal point of operation can be calculated using `calc_chiller_quality_grade()`
Do NOT use this function to determine the input for calc_cops()!
quality_grade = calc_chiller_quality_grade(nominal_conditions)
References¶
[1]  VDE ETG Energietechnik, VDEStudie “Potenziale für Strom im Wärmemarkt bis 2050  Wärmeversorgung in flexiblen Energieversorgungssystemen mit hohen Anteilen an erneuerbaren Energien”. 2015. (http://www.energiedialog2050.de/BASE/DOWNLOADS/VDE_ST_ETG_Warmemarkt_RZweb.pdf) 
[2] 
