Mechanical Plants allow engineers to create and customize a wide range of central equipment which circulates either heating, cooling, or condenser fluid through a building. These include boiler plants, chiller plants, central heat pump plants, and much more! Default 'ideal' plants are included on every project, these are auto-assigned to Air Systems and allow for sizing of Systems without the need to define a mechanical plant. Following are the detailed inputs for mechanical plants, follow links for more in-depth information.

Plant Sizing

  • Fluid Type: the type of fluid that's circulating through the plant loops. Options are: Water, Steam, Propylene Glycol, Ethylene Glycol

  • Glycol Concentration: percentage of glycol present in the plant loop fluid.

  • Max Temperature [°F (IP) | °C (SI)]: the maximum allowable temperature for the loop

  • Min Temperature [°F (IP) | °C (SI)]: the minimum allowable temperature for the loop

  • Max Flow Rate [GPM (IP) | L/S (SI)]: the maximum loop flow rate

  • Min Flow Rate [GPM (IP) | L/S (SI)]: the maximum loop flow rate

  • Load Distribution Scheme: selects the algorithm used to sequence equipment operation in order to meet the plant loop demand.

    Options are:

    • Optimal - operates each piece of equipment at its optimal part-load ratio. Any remaining loop demand is distributed evenly to all of the components

    • Sequential Load - loads each piece of equipment sequentially in the order specified in the Plant Equipment List to its maximum part load ratio and will operate the last required piece of equipment between its minimum and maximum part load ratio in order to meet the loop demand.

    • Uniform Load - evenly distributes the loop demand among all available components on the equipment list for a given load range. If some components do not have the capacity to meet the uniformly distributed load, the remaining load is distributed sequentially to the other available components.

    • Sequential Uniform PLR - evenly distributes the loop demand among all available components on the equipment list for a given load range. If some components do not have the capacity to meet the uniformly distributed load, the remaining load is distributed sequentially to the other available components.

    • Uniform PLR - will load all equipment on the Plant Equipment List to a uniform part load ratio (PLR). No equipment will be loaded below its minimum PLR. If the total load is less than the sum of all equipment on the Plant Equipment List operating at their respective minimum PLRs, then the last item in the equipment list is dropped and the load is distributed based on a uniform PLR for the remaining plant equipment

  • Sizing Option: Options are: Coincident, Non-Coincident

  • Coincident Sizing Mode: Options are: None, Global Heating Sizing Factor, Global Cooling Sizing Factor, Component Sizing Factor


Electric Chiller

  • Name: A unique name for the equipment can be provided

  • Type: determines what type of condenser will be modeled with this chiller.

  • Reference Capacity: the reference cooling capacity of the chiller at the specified temperatures and water flow rates. Defaults to Autosized.

  • Reference COP: the chiller’s coefficient of performance at the specified reference temperatures and water flow rates.

  • Leaving Chilled Water Temperature [°F (IP) | °C (SI)]: the chiller’s reference leaving chilled water temperature

  • Entering Condenser Water Temperature [°F (IP) | °C (SI)]: the chiller’s reference entering condenser fluid temperature

  • Chilled Water Flow Rate [GPM (IP) | L/S (SI)]: for a variable flow chiller this is the maximum water flow rate and for a constant flow chiller this is the operating water flow rate through the chiller’s evaporator.

  • Condenser Water Flow Rate [GPM (IP) | L/S (SI)]: the chiller’s operating condenser fluid flow rate

  • Minimum Part Load Ratio: the chiller’s minimum part-load ratio. Must be between 0 and 1, but less than or equal to the Maximum Part Load Ratio.

  • Maximum Part Load Ratio: the chiller’s maximum part-load ratio. This value may exceed 1, but the normal range is between 0 and 1.0. The Maximum Part Load Ratio must be greater than or equal to the Minimum Part Load Ratio.

  • Reference Part Load Ratio: the absorption chiller’s optimum part load ratio at which the chiller performs at its maximum COP.

  • Minimum Unloading Ratio: the chiller’s minimum unloading ratio. This is where the chiller capacity can no longer be reduced by unloading and must be false loaded to meet smaller cooling loads. Must be greater than or equal to the Minimum Part Load Ratio, and less than or equal to the Maximum Part Load Ratio

  • Internal Flow Mode: determines how the chiller operates with respect to the intended fluid flow through the device’s evaporator. Choices are:

    • Passive - useful for either variable or constant speed pumping arrangements where the chiller is passive in the sense that although it makes a nominal request for its design flow rate it can operate at varying flow rates.

    • Temperature Control - changes the chiller model to internally vary the flow rate so that the temperature leaving the chiller matches a setpoint.

    • Constant Flow - useful for constant speed pumping arrangements where the chiller’s request for flow is stricter and can increase the overall loop flow.

  • Priority: details the order in which the chiller is prioritized in the loop.


District Cooling Connection

  • Name: A unique name for the equipment can be provided

  • Nominal Capacity [Btu/h (IP) | Watts (SI)]: the nominal demand that the district cooling will meet. Defaults to Autosized.


Constant Pump Speed

  • Name: A unique name for the equipment can be provided

  • Location: If the pumping strategy is set to primary-secondary, this input will specify which loop the pump is located on.

  • Rated Flow Rate [GPM (IP) | L/S (SI)]: the pump’s design volume flow rate. Defaults to Autosized.

  • Rated Pump Pressure [psi (IP) | Pa (SI)]: the pump’s design head pressure.

  • Rated Power [Watts (IP/SI)]: the pump’s design power consumption.

  • Motor Efficiency: the pump motor’s efficiency in decimal form.

  • Control Type: Choices are:

    • Continuous - the pump will run regardless of whether or not there is a load. This may have the net effect of adding heat to the loop if no equipment is turned on.

    • Intermittent - the pump will run at its capacity if a load is sensed and will shut off if there is no load on the loop.


Variable Pump Speed

  • Name: A unique name for the equipment can be provided

  • Location: If the pumping strategy is set to primary-secondary, this input will specify which loop the pump is located on.

  • Rated Flow Rate [GPM (IP) | L/S (SI)]: the pump’s design volume flow rate. Defaults to Autosized.

  • Rated Pump Pressure [psi (IP) | Pa (SI)]: the pump’s design head pressure

  • Rated Power [Watts (IP/SI)]: the pump’s design power consumption. Defaults to Autosized.

  • Motor Efficiency: the pump motor’s efficiency in decimal form.

  • Minimum Flow Rate [GPM (IP) | L/S (SI)]: the minimum volume flow rate while operating in variable flow capacity rate. Defaults to Autosized.

  • Control Type: Choices are:

    • Continuous - the pump will run regardless of whether or not there is a load. This may have the net effect of adding heat to the loop if no equipment is turned on.

    • Intermittent - the pump will run at its capacity if a load is sensed and will shut off if there is no load on the loop.

  • Minimum Flow Fraction: the minimum fluid volumetric flow rate for pumps, specified as a fraction of the maximum fluid flow rate


Pumping Strategies

  • Pumping Strategy: Options are:

    • Primary - means that there is no secondary loop and the plant loop is modeled as a single primary loop.

    • Primary-Secondary Flow Control - means that the plant loop does not attempt any temperature control, it only satisfies secondary (demand side) flow requests.

    • Primary-Secondary Temperature Control - allows control of the secondary (demand side) inlet temperature or the primary (plant side) inlet temperature by placing a setpoint on the corresponding node.

  • Primary Pump Type: Specifies the type of pump placed on the primary plant loop. Options are: Variable, Constant

  • Secondary Pump Type: Specifies the type of pump placed on the secondary plant loop. Options are: Variable, Constant


Heating Hot Water Boiler

  • Name: A unique name for the equipment can be provided

  • Fuel Type: specifies the type of fuel used by the boiler. Options are: Electricity, Natural Gas, Propane, Fuel Oil #1, Diesel

  • Nominal Capacity [Btu/h (IP) | Watts (SI)]: the nominal operating capacity of the boiler. Defaults to Autosized.

  • Nominal Thermal Efficiency: the heating efficiency (as a fraction between 0 and 1) of the boiler’s burner. This is the efficiency relative to the higher heating value (HHV) of fuel at a part load ratio of 1.0

  • Design Fluid Flow [GPM (IP) | L/S (SI)]: the maximum design water volumetric flow rate. This should be the largest flow rate than can be heated.

  • Minimum Part Load Ratio: the boiler's minimum part-load ratio. Must be between 0 and 1, and less than or equal to the Maximum Part Load Ratio.

  • Maximum Part Load Ratio: the boiler’s maximum part-load ratio. This value may exceed 1, but the normal range is between 0 and 1.0. The Maximum Part Load Ratio must be greater than or equal to the Minimum Part Load Ratio.

  • Reference Part Load Ratio: the boiler's optimum part load ratio at which the boiler performs at its maximum COP.

  • Max Leaving Heating Hot Water Temperature Limit [°F (IP) | °C (SI)]: the outlet temperature upper limit.

  • Internal Flow Method: determines how the boiler operates with respect to the intended fluid flow through the device. Choices are:

    • Passive - useful for either variable or constant speed pumping arrangements where the boiler is passive in the sense that although it makes a nominal request for its design flow rate it can operate at varying flow rates.

    • Temperature Control - changes the boiler model to internally vary the flow rate so that the temperature leaving the boiler matches a setpoint.

    • Constant Flow - useful for constant speed pumping arrangements where the boiler’s request for flow is more strict and can increase the overall loop flow.

  • Priority: details the order in which the boiler is prioritized in the loop.


District Heat Connection

  • Name: A unique name for the equipment can be provided

  • Nominal Capacity [Btu/h (IP) | Watts (SI)]: the nominal demand that the district heating will meet. Defaults to Autosized.


Cooling Tower

  • Name: A unique name for the equipment can be provided

  • Tower Type: Dropdown menu with the following options

    • Single Speed: utilizes a single-speed fan to control exit water temperature.

    • Variable Speed: utilizes a variable speed fan to control exit water temperature.

  • Nominal Capacity [Btu/h (IP) | Watts (SI)]: This numeric input field contains the “nominal” heat rejection capacity of the cooling tower in watts

  • Design Water Flow Rate [GPM (IP) | L/S (SI)]: This numeric field contains the design water flow rate through the tower. This value is the flow rate of the condenser loop water being cooled by the tower (not the flow rate of water being sprayed on the outside of the heat exchange coil)

  • Design Fan Power [hp (IP) | Watts (SI)]: This numeric field contains the fan power at the design air flow rate specified in the previous field. A value greater than zero must be specified.

  • Design Air Dry Bulb Temperature [°F (IP) | °C (SI)]: This numeric field specifies the inlet air dry-bulb temperature (˚C) at design conditions.

  • Design Air Wet Bulb Temperature [°F (IP) | °C (SI)]: This numeric field specifies the inlet air wet-bulb temperature (˚C) at design conditions. This design temperature should correspond with the design values for range temperature, approach temperature, water flow rate, and airflow rate specified in the following fields.

  • Design Approach Temperature [°F (IP) | ∆°C (SI)]: This numeric field specifies the tower approach temperature (˚C) at design conditions. The approach temperature is the outlet water temperature minus the inlet air wet-bulb temperature.

  • Design Range Temperature [∆°F (IP) | ∆°C (SI)]: This numeric field specifies the range temperature (˚C) at design conditions. The range temperature is defined as the inlet water temperature minus the outlet water temperature.

Video Tutorial

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