Figure 2 - 1 : HVAC components toolbar
ApacheHVAC provides for modeling a comprehensive range of HVAC components, as listed below.
Waterside plant equipment and water loops
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Heat sources: hot-water loops and pumps, equipment sequencing, boilers, generic heat sources, air-source heat pumps, solar hot-water, furnaces, electric-resistance heat, etc.
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Chilled water loops: sequenced operation of chillers and other cooling equipment, primary and secondary chilled-water loops, pumps, condenser loops, cooling towers, wet or dry fluid coolers, condenser heat recovery, integrated waterside economizer, etc.
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Chillers: electric water-cooled, air-cooled, other similar water cooling sources
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Waterside economizers (integrated, non-integrated, or dedicated)
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Water-source heat pump upgrade of heat recovered from a condenser-loop
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Air-to-air heat pumps (1 to 1 relationship with coil on airside; backup heat source)
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Direct-expansion (DX) cooling (1 to 1 relationship with a coil on the airside network)
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Unitary cooling systems (complete unit is represented by a coil on the airside network)
Airside plant equipment and system components
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Room components (representing any geometric/thermal space in the model)
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Heating coils (simple and advanced models for hot-water, generic, and AAHP sources)
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Cooling coils (simple and advanced models for chilled-water, DX, WSE, and UCS sources)
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Air-to-air heat/energy/enthalpy recovery devices
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Spray chamber humidifiers
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Steam injection humidifiers
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Damper sets, including mixing dampers and controlled flow splitters
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Ductwork components with thermal properties for modeling heat gain or loss
Room units – zone equipment applied within Room components
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Radiators and similar terminal heating devices, such as baseboard heaters
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Direct-acting heater/coolers
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Chilled ceiling panels, chilled beams, and similar terminal cooling devices
The first set of these are defined mainly in plant equipment dialogs. Components in the middle set are dealt with mainly on the airside network. The last set, room units, differ from other HVAC components in that they are defined in terms of “types” but then located within a room component or thermal zone (including in non-occupied space or a heated or cooled slab zone) rather than on the airside network.
The modeling of plant components is quasi-steady-state in that the program does not attempt to model transient behavior between simulation time steps. However, because time steps in ApacheSim are typically only 6-10 minutes, and can be as little as 1 minute, if desired, constant plant behavior over a time step is an appropriate assumption. Furthermore, there is interaction between the HVAC system and conditioned spaces (including natural ventilation, stack-vent double-skin facades, etc. when running MacroFlo) at every simulation time step.
The solution algorithm also provides for modeling intentionally undersized heating and cooling plant equipment or sources. Coils and other connected devices on a hot or chilled water loop will receive off-design water loop temperatures in keeping with the capability of the modeled plant equipment when the load exceeds the heating or cooling capacity.
Data entered for fans represents a special case in that fans are not controlled directly and fan component inputs are used only to calculate consequential energy consumption and effect on air temperature. The value entered in a fan component does not determine airflow through the system. Rather, the fan component acts like a meter with a defined set of performance characteristics. The airflow through the fan is determined by flow controllers on network branches.
All pre-defined HVAC equipment performance curves, such as those provided for Electric Water-Cooled Chillers, DX Cooling, Hot-Water Boilers, and Water-to-Air Heat Pumps, are valid only at the reference or Rated conditions that were used to derive the curves from the performance data. (Reference condition is the condition to which all other performance data are normalized.) The default Rated condition temperatures—for example, the rated entering condenser water temp and rated chilled water supply temperature for the EWC chillers—as shown in the Rated condition tab of the chiller editing dialog are those used as the reference conditions for the currently selected set of performance curves. Therefore, except when intending either to edit the performance curves or add new performance curves based on different reference condition temperatures, avoid editing the default rated condition temperatures.
Loads and sizing data for room/zone loads, ventilation rates, zone/terminal equipment, primary airside equipment, and heating and cooling plant are provided in design sizing reports.
Simulation results are provided for each reporting time step (1 hour maximum; 6 minutes minimum). Results are reported separately for each plant equipment category and fuel/energy type. Coil psychrometrics can be assessed for each time step. Thermal, moisture, and air flow results for each airside node can be queried for individual time steps. Energy used by room units at each time step is accounted for and reported separately from airside HVAC heating and cooling components.
Room units can be added to spaces contained within HVAC zones as well as directly to spaces in an un-zoned model. It is recommended that users work with Room components within ApHVAC, instead of Zone components, when large numbers of room units are to be implemented as editing of the units will be quicker and more efficient.
