VRF Condenser Unit (Air Cooled)

Variable Refrigerant Flow (VRF) Condenser Unit (Air Cooled) regulates cooling by adjusting refrigerant flow based on demand, ensuring precise temperature control. The air-cooled design enhances efficiency by dissipating heat through air exchange.

Sizing

Cooling – Rated COP

Specify the Cooling – Rated COP, indicating the cooling coefficient of performance at rated conditions. This COP includes compressor power and condenser fan power, excluding impacts due to the supply air fan. The nominal heat pump cooling COP should be greater than 0 and less than 10.

Heating – Rated COP

Specify the Heating – Rated COP, representing the heating coefficient of performance at rated conditions. This COP includes compressor power and condenser fan power, excluding impacts due to the supply air fan. The nominal heat pump heating COP should be greater than 0 and less than 10.

Heating Capacity Sizing Ratio

Specify the Heating Capacity Sizing Ratio, denoting the gross heating to gross cooling capacity ratio.

Min. Heat Pump Part Load Ratio

Specify the Min. Heat Pump Part Load Ratio, indicating the heat pump's minimum operating part-load ratio (PLR). When the heat pump operates at a PLR below this value, the compressor will cycle to meet cooling or heating demand.

Sizing Method

Specify the Sizing Method by choosing between Autosize or manual. Autosize utilizes Energy Plus sizing routines, while manual entry provides detailed component sizing information.

Gross Rated Total Cooling Capacity

Specify the Gross Rated Total Cooling Capacity, denoting the total cooling capacity (sensible + latent) of the heat pump at rated conditions in watts.

Gross Rated Heating Capacity

Specify the Gross Rated Heating Capacity, indicating the gross total heat pump heating capacity at rated conditions in watts. The nominal heat pump heating capacity must be greater than 0.

Min. Condenser Inlet Temp. - Cooling Mode

Specify the Min. Condenser Inlet Temp. - Cooling Mode, defining the minimum source inlet temperature allowed for cooling operation. For air-cooled equipment, outdoor dry-bulb temperature is used, and for water-cooled equipment, inlet water temperature is used. Cooling is disabled below this temperature. If left blank, the default value is -6∘C.

Max. Condenser Inlet Temp. - Cooling Mode

Specify the Max. Condenser Inlet Temp. - Cooling Mode indicates the maximum source inlet temperature allowed for cooling operation. For air-cooled equipment, outdoor dry-bulb temperature is used, and for water-cooled equipment, inlet water temperature is used. Cooling is disabled above this temperature. If left blank, the default value is 43∘C.

Min. Condenser Inlet Temp. - Heating Mode

Specify the Min. Condenser Inlet Temp. - Heating Mode, defining the minimum source inlet temperature allowed for heating operation. For air-cooled equipment, outdoor dry-bulb temperature is used, and for water-cooled equipment, inlet water temperature is used. The heating is disabled below this temperature. If left blank, the default value is -20∘C.

Max. Condenser Inlet Temp. - Heating Mode

Specify the Max. Condenser Inlet Temp. - Heating Mode denotes the maximum source inlet temperature allowed for heating operation. For air-cooled equipment, outdoor dry-bulb temperature is used; water-cooled equipment uses inlet water temperature. The heating is disabled above this temperature. If left blank, the default value is 16∘C. Manufacturers' specifications should be checked for water-cooled equipment, and a more reasonable value may need to be entered.

Number of Compressors

Specify the Number of Compressors in the heat pump condensing unit, used to determine the operating characteristics of the crankcase heater.

Ratio Compressor Size to Compressor Capacity %

Specify the Ratio Compressor Size to Compressor Capacity %, a numeric field defining the size of the first stage compressor to the total compressor capacity. This parameter is exclusively used for calculating crankcase heater energy, with a default value of 0.5.

Piping

Piping Length – Cooling Mode

Specify the Piping Length – Cooling Mode, representing the equivalent pipe length in meters between the farthest terminal unit and the heat pump condenser. This includes gas refrigerant line length, fitting losses, pipe bends, and other connections contributing to piping losses.

Piping Length – heating Mode

Specify the Piping Length – Heating Mode, indicating the equivalent pipe length in meters between the farthest terminal unit and the heat pump condenser. This value encompasses liquid refrigerant line length, fitting losses, pipe bends, and other connections contributing to piping losses.

Piping Height

Specify the Piping Height, representing the vertical pipe height in meters between the highest or lowest terminal unit and the heat pump condenser. This value defines gravitational losses due to height changes between the highest (positive value) or lowest (negative value) terminal unit and the heat pump condenser.

Piping Height Correction Factor - Cooling Mode

Specify the Piping Height Correction Factor - Cooling Mode, representing the vertical pipe height in meters between the highest or lowest terminal unit and the heat pump condenser. This factor defines gravitational losses due to changes in height between the highest (positive value) or lowest (negative value) terminal unit and the heat pump condenser.

Piping Height Correction Factor - Heating Mode

Specify the Piping Height Correction Factor - Heating Mode, indicating the equivalent pipe length in meters between the farthest terminal unit and the heat pump condenser. This value includes liquid refrigerant line length, fitting losses, pipe bends, and other connections contributing to piping losses.

Heat Recovery

Heat Pump Waste Heat Recovery

Specify the Heat Pump Waste Heat Recovery configuration, choosing between Yes and No. If Yes is selected, heat recovery is enabled, allowing the heat pump to independently cool and heat different zones. If No is chosen, the heat pump can only cool or heat during any given time step.

Min. Condenser Inlet Temp. - Heat Recovery Mode

Specify the Min. Condenser Inlet Temp. - Heat Recovery Mode, indicating the minimum source inlet temperature allowed for heat recovery operation. Heat recovery is disabled below this temperature.

Max. Condenser Inlet Temp. - Heat Recovery Mode

Specify the Max. Condenser Inlet Temp. - Heat Recovery Mode, setting the maximum source inlet temperature allowed for heat recovery operation. Heat recovery is disabled above this temperature. This input must be less than the smaller of the maximum condenser inlet node temperature in cooling or heating mode.

Initial Heat Recovery Cooling Capacity Fraction

Specify the Initial Heat Recovery Cooling Capacity Fraction, representing the heating capacity time constant in hours. This parameter models the time it takes for the system to transition from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants.

Heat Recovery Cooling Capacity Time Constant

Specify the Heat Recovery Cooling Capacity Time Constant, representing the cooling capacity time constant in hours. This parameter models the time it takes for the system to transition from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants.

Initial Heat Recovery Cooling Energy Fraction

Specify the Initial Heat Recovery Cooling Energy Fraction, indicating the heating capacity time constant in hours. This parameter models the time it takes for the system to transition from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants.

Heat Recovery Cooling Energy Time Constant

Specify the Heat Recovery Cooling Energy Time Constant, representing the cooling energy time constant in hours. This parameter models the time it takes for the system to transition from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants.

Initial Heat Recovery Heating Capacity Fraction

Specify the Initial Heat Recovery Heating Capacity Fraction, indicating the fraction of heating energy consumed when the system changes from heating-only operation to simultaneous heating and cooling. It is common for the heating energy to decrease before the system recovers.

Heat Recovery Cooling Capacity Time Constant

Specify the Heat Recovery Cooling Capacity Time Constant, representing the cooling capacity time constant in hours. This parameter models the time it takes for the system to change from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants.

Initial Heat Recovery Heating Energy Fraction

Specify the Initial Heat Recovery Heating Energy Fraction, representing the heating capacity time constant in hours. This parameter models the time it takes for the system to transition from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants.

Heat Recovery Heating Energy Time Constant

Specify the Heat Recovery Heating Energy Time Constant, defining the heating energy time constant in hours. This parameter models the time it takes for the system to change from cooling-only operation to simultaneous cooling and heating, with a total response time defined as 5 time constants. If this field is left blank, a default value of 0.0 is used.

Defrost

Crankcase Heater Power Per Compressor

Specify the Crankcase Heater Power Per Compressor, indicating the electrical power consumed by the crankcase heater in watts for each compressor. This heater operates when the outdoor temperature is below the maximum outdoor dry-bulb temperature for crankcase heater operation. The minimum value for this field is 0, and if left blank, the default value is 33 watts.

Max. Outdoor Temp. for Crankcase Heater

Specify the Max. Outdoor Temp. for Crankcase Heater, defining the maximum outdoor temperature in degrees Celsius below which the crankcase heater will operate. If left blank, the default value is 0 degrees Celsius. Note that this field only calculates crankcase heater power and doesn't impact heat pump performance.

Defrost Strategy

Specify the Defrost Strategy, with options of reverse-cycle or resistive. In reverse-cycle, the heating cycle is periodically reversed to melt frost on the outdoor coil, while resistive uses an electric resistance heater. If left blank, the default is reverse-cycle. Defrost can be disabled by entering a resistive defrost strategy with a timed defrost control, 0 defrost time period fraction, and 0 resistive defrost heater capacity if the Maximum Outdoor Dry-Bulb Temperature for Defrost Operation is greater than the expected minimum outdoor dry-bulb temperature.

Defrost Control

Specify the Defrost Control, choosing between timed or on-demand. Timed control calculates the defrost time period based on a fixed value of compressor runtime, whether frost has accumulated or not. If using timed defrost control, input the fractional amount of time the unit is in defrost in the "Defrost Time Period Fraction" field.

Defrost Time Period Fraction

Specify the Defrost Time Period Fraction, indicating the fraction of compressor runtime when the defrost cycle is active. For instance, if the defrost cycle is active for 3.5 minutes every 60 minutes of compressor runtime, enter 3.5/60 = 0.058333. Ensure this value is greater than or equal to 0.

Defrost Heater Capacity

Specify the Defrost Heater Capacity, defining the capacity of the resistive defrost heating element in Watts. This field is applicable only when the chosen defrost strategy is 'resistive'. The value must be greater than or equal to 0, and if left blank, the default value is 0.

VRF Condenser Unit Curves

Cooling Capacity Ratio Boundary

Separates low and high cooling capacity ratio performance curves by calculating outdoor dry-bulb temperature from weighted average indoor wet-bulb temperature.

Cooling Capacity Ratio Modifier Function of High Temperature

High outdoor temperature performance curve for cooling capacity ratio. Use when a single curve can't accurately model performance across all temperatures.

Cooling Capacity Ratio Modifier Function of Low Temperature

Models full load cooling capacity ratio as a function of outdoor dry-bulb and indoor wet-bulb temperatures. Supports up to two curves for complex performance profiles.

Cooling Combination Ratio Correction Factor

Adjusts rated capacity when total indoor terminal unit cooling capacity exceeds the system's Gross Rated Total Cooling Capacity.

Cooling Energy Input Ratio Boundary

Separates low and high cooling energy input ratio performance curves by calculating outdoor dry-bulb temperature from weighted average indoor wet-bulb temperature.

Cooling Energy Input Ratio Modifier Function of High Part Load Ratio

Models cooling energy ratio for part-load ratios above 1 (possible in variable speed compression systems).

Cooling Energy Input Ratio Modifier Function of High Temperature

High outdoor temperature performance curve for cooling energy ratio. Use when a single curve doesn't capture the full temperature range accurately.

Cooling Energy Input Ratio Modifier Function of Low Part Load Ratio

Models cooling energy ratio for part-load ratios at or below 1.

Cooling Energy Input Ratio Modifier Function of Low Temperature

Models cooling energy ratio as a function of outdoor dry-bulb and indoor wet-bulb temperatures.

Cooling Part Load Fraction Correlation

Accounts for cycling losses when the compressor cycles on and off below the Minimum Heat Pump Part-Load Ratio.

Heating Capacity Ratio Boundary

Separates low and high heating capacity ratio performance curves by calculating outdoor dry-bulb or wet-bulb temperature from weighted average indoor dry-bulb temperature.

Heating Capacity Ratio Modifier Function of High Temperature

High outdoor temperature performance curve for heating capacity ratio. Use when a single curve doesn't cover all temperature conditions.

Heating Capacity Ratio Modifier Function of Low Temperature

Models full load heating capacity ratio as a function of outdoor wet-bulb (or dry-bulb if unavailable) and indoor dry-bulb temperatures.

Heating Combination Ratio Correction Factor

Adjusts rated capacity when total indoor terminal unit heating capacity exceeds the Gross Rated Heating Capacity.

Heating Energy Input Ratio Boundary

Separates low and high heating energy input ratio performance curves by calculating outdoor dry-bulb or wet-bulb temperature from weighted average indoor dry-bulb temperature.

Heating Energy Input Ratio Modifier Function of High Part Load Ratio

Models heating energy input ratio for part-load ratios above 1.

Heating Energy Input Ratio Modifier Function of High Temperature

Allows separate performance curves for heating energy at high temperatures.

Heating Energy Input Ratio Modifier Function of Low Part Load Ratio

Models heating energy input ratio for part-load ratios below 1.

Heating Energy Input Ratio Modifier Function of Low Temperature

Models heating energy ratio as a function of outdoor wet-bulb (or dry-bulb if unavailable) and indoor dry-bulb temperatures.

Heating Part Load Fraction Correlation

Accounts for cycling losses when the compressor cycles on and off below the Minimum Heat Pump Part-Load Ratio.

Piping Correction Factor for Length in Heating Mode

Defines coefficients (a0, a1, a2, a3, a4) for the piping correction factor equations:

• PCF = a0 + a1×L + a2×L² + a3×L³ + a4×H

• PCF = a0 + a1×L + a2×L² + a3×CR + a4×CR² + a5×(L×CR)

where L = pipe length, H = height difference, and CR = combination ratio.

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