Heat Pump - Cooling

 

The Equation fit model uses four non-dimensional equations (curves) to predict the heat pump performance in cooling and heating modes. The methodology involves using the generalised least square method to generate a set of performance coefficients from the catalogue data at indicated reference conditions. Then the respective coefficients and indicated reference conditions are used in the model to simulate the heat pump performance. The variables that influenced the water-to-water heat pump performance are load side inlet water temperature, source side inlet temperature, source side water flow rate and load side water flow rate.

General

Template

You can load data to the dialog from a pre-defined heat pump template as a starting point for your particular heat pump component. A sample list of manufacturers data is provided in the templates and instructions on how to create your own templates from manufacturers data.

 

Heat pumps are usually selected using their Rated cooling capacity.

Reference COP

This field is required if the Reference cooling power consumption is set to autosize. The nominal COP is defined by the Reference cooling capacity divided by the corresponding Reference cooling power consumption and is non-dimensional. This field is only used for sizing; if the Reference power consumption is set to a fixed value then the COP of the component during simulation will be determined by the ratio of Reference cooling capacity divided by the corresponding Reference cooling power consumption and not by the value in this field. This COP does not include power for fluid circulation pumps, it is just for the heat pump itself.

Sizing factor

This optional numeric field allows a sizing factor for this component to be specified. The sizing factor is used when the component design inputs are autosized: the autosizing calculations are performed as usual and the results are multiplied by the sizing factor. The Sizing factor allows a component to be sized to meet part of the plant loop’s design load while continuing to use the autosizing feature. For example if there are two heat pumps on the supply side, each one could be sized to be half of the design load.

Rated Flow Rate and Capacity

Reference load side flow rate

This numeric field contains the rated volumetric flow rate on the load side of the heat pump in (m3/s or gal/min). This corresponds to the highest load side heat transfer rate listed in the catalogue data.

Reference source side flow rate

This numeric field contains the rated volumetric flow rate on the source side of the heat pump in (m3/s or gal/min). This corresponds to the highest load side heat transfer rate listed in the catalogue data.

Reference cooling capacity

This numeric field contains the rated cooling capacity of the heat pump in W. This corresponds to the highest load side heat transfer rate listed in the catalogue data.

Reference cooling power consumption

This numeric field contains the rated power consumption of the heat pump in W. This corresponds to the highest load side heat transfer rate listed in the catalogue data.

v7.3 only

Cooling Capacity Coefficients

Five fields are used to describe the coefficients for the Cooling Capacity curve. More details on how these coefficients are used are provided in the technical section of the Plant loop heat pumps page and in the Engineering Reference.

Cooling capacity coefficient 1-5

These numeric fields contain the five coefficients for the heat pump capacity.

Cooling Compressor Power Coefficients

Five fields are used to describe the coefficients for the Cooling Compressor Power consumption curve. More details on how these coefficients are used are provided in the technical section of the Plant loop heat pumps page and in the Engineering Reference.

Cooling compressor power coefficient 1-5

These numeric fields contain the five coefficients for the heat pump power consumption.

Advanced

Cycle time

The full on and off cycle time of the heat pump unit in hours. You are advised to leave this data at the default value of 0.0161 hours (1 minute) which is also the minimum value. The maximum allowed value is 0.1 hours (6 minutes) but note that using values higher than the default can prevent correct operation of the heat pump.

v8 only

Performance Curves

Cooling capacity curve

Select a quadlinear Performance curve object to be used to define the cooling capacity of this heat pump at runtime.

 

More details on how these coefficients are used are provided in the technical section of the Plant loop heat pumps page and in the Engineering Reference.

Cooling compressor power curve

Select a quadlinear performance curve object to define the Cooling compressor power curve. More details on how these coefficients in the curve are used are described in the Engineering Reference.

Companion Component

Companion heating heat pump

This optional selection allows you to specify the companion heating water to water heat pump for this cooling component. This should be the name of an Equation Fit heat pump heating component on the same plant loop. Because the cooling and heating models are often intended to represent separate operating modes of one single reversible heat pump, it is useful to identify the corresponding heating heat pump. This is used with autosizing so that the sizing calculations can be coordinated ensuring that the two companion heat pumps get the same design reference flow rates.

 

The plant loop EIR model is based on the same formulation used in the EIR chiller model. This allows curves specifying capacity and energy usage to be defined generically, enabling them to be applicable to a wide variety of components. In this model, the curve can be a quadratic function of temperatures or an even more generic lookup table.

Tip: Note: The EIR model is more flexible than the Equation fit model. It can be operated either as a water-sourced heat pump with the source side connected to another plant loop or as an air-sourced heat pump with the source side interacting with the outdoor air.

Data for this component is also considered to be easier to obtain than for the Equation fit model.

Note: This component is currently a constant flow device (it will always request its full design flow from the plant). A future addition is planned to make it respond to outlet setpoint in order to vary the flow request.

General

Reference COP

This field contains the reference COP for this unit, which is used when calculating the power required for the heat pump under simulation conditions. The COP is defined as the load side energy transfer divided by the power input, with dimensionless units of [W/W].

Sizing factor

This field allows the user to scale the sizing of this unit compared to the plant-determined autosized flow and heat capacity.

Flow Rates and Capacity

Load side reference flow rate

This autosizable setting defines the reference load side flow rate for the heat pump. This field is used as the nominal flow request for this heat pump unit during the simulation. The units for this field are (m3/s or gal/min).

Source side reference flow rate

This autosizable setting defines the reference source side flow rate for the heat pump. This field is used as the nominal flow request for this heat pump unit during the simulation. The units for this field are (m3/s or gal/min).

Important Note: For air source heat pumps, the Source side reference flow rate is an air flow rate, whereas for water to water heat pumps it is a water flow rate. Water source side reference flow rates will typical be much lower than Air source reference air flow rates.

Reference capacity

This autosizable setting defines the heat pump's reference load side cooling capacity (in W).

Performance Curves

Capacity modifier function of temperature curve

Select a bivariate curve or table that defines an available capacity modifier of the unit as a function of the load side outlet temperature and the source side inlet temperature. The temperatures are in °C when used in the function and the output of the function is multiplied by the reference capacity to get a current available capacity.

Electric input to output ratio modifier function of temperature curve

Select a bivariate curve or table that defines an EIR (1/COP) modifier as a function of the load side outlet temperature and the source side inlet temperature. The temperatures are in °C when used in the function. The output of this function and the output of the EIR Modifier Function of PLR are multiplied by the reference EIR to get a current EIR .

Electric input to output ratio modifier function of part load ratio curve

Select a univariate curve or table that defines an EIR modifier as a function of the current part load ratio. The output of this function and the output of the EIR Modifier Function of Temperature are multiplied by the reference EIR to get a current EIR .

Condenser

Condenser type

Select the heat pump’s condenser type. Options are:

 

• 1-Air Source - for an air to water heat pump

• 2-Water Source for a water to water heat pump