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IEA HPP Annex 28
Calculation method
Workshop IEA HPP Annex 288th International Heat Pump Conference, Las Vegas, 30 May 2005
Carsten Wemhöner, Operating Agent IEA HPP Annex 28
Institute of Energy, University of Applied Sciences Basel
2
Outline of the presentation
Objectives
Extension to combined systems
Simplifications, calculations steps and input data
Principle of the calculation
3
Objectives of the calculation method Transparent
no correction factors as far as possible
Easy-to-use “hand calculation”, no extensive computer application or simulation suited for standards
Based on publicly available data standard testing results component characteristics from technical data sheets
Applicable to the majority of systems on the market
4
Calculation method – basic situation
Output capacity and efficiency (COP) strongly dependent on source and sink temperature and changes over the operation range
Output capacity and efficiency (COP) are known at defined testing points (from standard component testing)
Meteorological data available for evaluation of the source temperature
Controller settings available for the characterisation of the sink temperature
Annual energy requirement for space heating and domestic hot water are known from standard calculations (building regulations)
5
Principle of the calculation method
Annual frequency of the ambient dry bulb air temperature
ambient dry bulb temperature [°C]
Cumulative annual frequency of the ambient dry bulb air temperature
Meteo data processing
6
3
Principle of the calculation method
ambient dry bulb temperature [°C]
Bin distribution
Operation conditions at the operating points valid for the entire bin
Bins should have connection to available information on the heat pump characteristic
Conclusion: Operating point in the centre of the bin
Bin limits between operating points
Design indoor temperature
OP1
OP3
OP2
design outdoortemperature
3, upper
3, lower
Upper ambient temperature for heating
7
Performance factor at operating point
Efficiency values from standard testing valid for the whole bin COP interpolated for the conditions at the operating point
Further system losses Storage losses
Additional electrical auxiliary expense heat pump auxiliaries not considered in the COP boundary (e.g. brine source
pump) Circulation pumps Control only in times when heat pumps is not running
PFi = Qnet,i + Qloss,i
COPi
Qnet,i
+ Eaux,i
Qnet,i
COPi
Qnet,i
8
Principle of the calculation method
Measure for the energy requirement:Heating degree hours(HDH)
Energy requirement
Heating degree hours=
dt)( aID
Energy requirement in the bin corresponds to difference of cumulative heating degree hours at bin limit
Area of the bin (area between cumulative frequency and indoor design temperature) corresponds to energy requirement
Relative energy requirement in the bin corresponds to ratio of bin areas(weighting factor)
Operation conditions at operating point valid for the entire bin
3
ambient dry bulb temperature [°C]
Design indoor temperature
OP1
OP3
OP2
design outdoortemperature
3, upper
3, lower
Upper ambient temperature for heating
ID
a
dt
HP2
HP1
HP3
9
Seasonal performance factor of heat pump
Seasonal performance by summation over all bins
Electricity input can be expressed with performance factor SPFhp =
iQnet,i
i PFi
iEi
Ratio between bin heat requirement
and total heat requirement can be
expressed by weighting factor
Qnet1
·Qnet
wiQnet,i
10
Principle of the calculation methodBack-up energy
ambient dry bulb temperature [°C]
Design indoor temperature
OP1
OP3
OP2
design outdoortemperature
Upper ambient temperature for heating
HP2
HP1
HP3 Mixed operation mode
heat pump is switched- off at low temperature cut-out
BU
HP1
BUBU
Balance point temperature
Alternate operation modeheat pump is switched- off at balance point
Operation of the back-up heating defined by Operation mode Balance point
temperature Low temperature cut-
out
Parallel operation modeheat pump runs through
low temperature cut-out
11
Seasonal performance factor of heating mode
Overall performance of heat pump and back-up heating by weighting with delivered energy fractions
SPFh =Qhp
SPFhp
EhpQhp
+ Qbu
+ Ebu+ Qbu
bu
Qnet
12
W3
Principle of the calculation method
ambient dry bulb temperature [°C]
OP2
OP1
Upper ambient temperature for heating
BU
OP3
design outdoortemperature
Balance point temperature
HP
HP
HP
W2
W1
Design indoor temperature
Domestic hot water
Combination of different operation modes by weighting with the respective energy fractions
Approach: Daily tapping profile Hot water energy
dependent on bin time
Back-up energy of domestic hot water mode is determined by temperature level (operation limit heat pump)
Evaluation of heat pump characterstic based on DHW-testing
W4OP4
13
Extension to combined systems
Alternate combined operating systems (heat pump switched):
Calculation of space heating and domestic hot water part
Superposition of single operation modes with weighting of energy fractions
Result from testing:characteristic does not change significantly
14
Extension to combined systems
Simultaneous combined operating systems (heat extraction):
Characteristic in simultaneous operation changes significantly!
Three operation modes have to be considered: Single space heating (e.g. winter operation, DHW storage entirely loaded) Single domestic hot water (e.g. summer operation) Simultaneous space heating and domestic hot water (SH and DHW demand)
Fraction of operation in each operation mode by evaluating the running time
15
Extension to combined systems
Running time t: produced heat/output capacity Maximum running time in combined operation
If tSH > tDHW
=> tcombi = tDHW => DHW operation limiting factor for simultaneous operation
If tDHW > tSH
=> tcombi = tSH => SH operation limiting factor for simultaneous operation
Either space heating (intermediate season) or DHW (winter) could be the limiting factor for combined operation
Maximum value may not be reached due to control effects and not necessarily simultaneous load requirement
16
Overall seasonal performance factor
As in the alternate case
the overall seasonal performance of simultaneous operation is calculated
Weighting of the performance factors of the operation modes
SPF =Qh
Qh
SPFh
+ QDHW
SPFDHW
QDHW
SPFcombi
Qcombi++
with the respective energy fraction
17
Assumptions/Simplifications
Main impact on space heating is outside temperature
Effects of intermittent heating included in the calculation of energy requirement (EN ISO 13790)
defrosting considered in the heat pump characteristic (e.g. EN 14511)
Domestic hot water requirement constant over the year (daily consumption)
Control effect cannot entirely be described but is reflected by standard situations
18
Calculation steps
Determination of energy requirement per bin
Determination of fraction by back-up energy (bivalent operation)
Interpolation of output capacity and COP for source and sink temperature
Correction for part load operation
Evaluation of running time in different operation modes
Calculation of auxiliary energy
Calculation of generator losses (recoverable/recovered)
Calculation of total energy input, system seasonal performance
19
Input data
Data of the site Meteorological data (i.e. hourly values of the outside temperature,
irradiation) Source temperature (e.g. outside air, ground, ground water etc.)
Energy Requirements Space heating energy requirement Domestic hot water energy requirement
Heat pump Type of the heat pump (e.g. brine-to-water, outside-air-to-water etc.) Heat pump characteristic (standard testing, e.g. EN 14511, ASHRAE 116 etc.) Operation limits
20
Input data
System design Controller settings (heating characteristic curve, upper temperature
limit for heating) Balance point (input or based on design heat load)
System components characteristics Installed storages (heating buffer, domestic hot water) Back-up generators (electrical, fossil) Domestic hot water operation (independent/alternate/combined) Nominal power of auxiliaries (pumps, fans, control…)
21
Thank you for your attention!