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quick overview of some TRNSYS examples

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HVAC Example 1 – Simple Absorption Chiller Analysis
Quick Overview:
This project illustrates the simulation of a simple chilled water distribution system in TRNSYS. A double-effect, hot-water fired absorption chiller acts as the base load chiller (meeting the majority of the cooling loads) while a single-effect, direct-fired absorption chiller (less efficient, but cheaper than the double-effect machine) acts as the peaking chiller (meeting the peak loads that the base-load chiller couldn’t meet). The loads that the chillers must meet are from a simple equation-based load model and not from a detailed building analysis; although a detailed model could easily be added to this project by the user.

Models Used:
Type 14 Forcing Function Type 31 Pipe Type 65 Online Plotter (2) Type 149 Constant Speed Pump (2) Type 198 Proportional Boiler Type 262 N-Stage Cooling Thermostat Type 274 Double-Effect, Hot-Water Fired Absorption Chiller Type 278 Single-Effect, Direct-Fired Absorption Chiller Type 279 Load-Imposed Flow Model

Detailed Description:
Type 14 Forcing Function: The forcing function model is used to set a profile of weekdays (function value = 1) and weekend days (function value = 0) in a repeating weekly cycle. This function value is sent to the equation component in order to calculate the building loads for weekdays and weekends.

Equation: The equation component in this simulation is used to calculate the building loads as a function of time and day type (weekday or weekend). The equation for the building load as a function of time is:
Building Load = Weekday *(5000000 + 3000000 * sin(Hour*180/12-90) + (1-Weekday) * (3000000 + 1000000 * sin(Hour*180/12-90))

where Weekday is the weekday control function from Type 14. The loads from this equation are plotted below in Figure 1.

Figure 1 Type 31 Pipe: The pipe model in this simulation is just used to give the simulation some thermal capacitance to avoid convergence problems in the solution. The losses from the pipe model are not considered for this simulation.

Type 279 Load-Imposed Flow: In many simulations, it is desired to impose a building heating or cooling load on a working fluid without having to model a detailed coil or air distribution system. This component is intended to handle these exact circumstances. In this simulation, the building cooling load energy is added to the working fluid as it returns to the chillers; resulting in a temperature rise of the working fluid that must be met by the chillers.

Type 262 N-Stage Cooling Thermostat: The thermostat model in this simulation senses the temperature of the water returning to the chillers and sends on/off control signals to the two absorption chillers. At low values of the return water temperature, the thermostat calls for only the double-effect base load chiller to operate. However at higher building loads, the double-effect chiller cannot meet the entire building load and the temperature of the returning fluid begins to rise. At this point, the thermostat will call for the single-effect chiller to turn on in order to bring the fluid temperatures back down. This thermostat model employs hysteresis in order to control the fluid temperatures in the loop; turning on at a certain temperature and staying on until another temperature condition has been reached.

Type 149 Chilled Water Pump: The constant-speed chilled water pump supplies the two absorption chillers (connected in series) with fluid during the simulation. The pump is set to be on constantly during the simulation, but could have been controlled by the last output of the thermostat model or by a simple equation that initiates the pump whenever the cooling load is positive. The one item to remember when using the pump model is that the pump sets the flow for the entire fluid loop by multiplying the rated flow rate (a parameter) by the on/off pump control signal (an input). The flow rate into this model is just used for convergence checking.

Type 274 Double-Effect, Hot-Water Fired Absorption Chiller: The base load chiller in this simulation is a double-effect, hot-water fired absorption chiller. The absorption chiller uses a hot water stream at high temperature to cool a chilled water stream. The energy absorbed from the hot water stream plus the energy removed from the chilled water stream are rejected to a cooling water stream. In most simulations, the cooling water stream rejects its energy to the ambient by the use of a cooling tower. However, in order to make this simulation easier to understand, the cooling water inlet temperature and flow rate to the chiller are assumed to be constant; taking their initial value of the inputs for the duration of the simulation. A simple addition of a cooling tower model and cooling water pump (controlled to operate when the chiller is operating) would make this simulation more realistic. The chiller modulates to meet the cooling load; attempting to cool the chilled water stream to the userdefined setpoint temperature given the available capacity. The capacity of the machine, along with the efficiency of the machine, are read from supplied data files containing the manufacturers catalog data as a function of the entering hot water temperature, the entering cooling water temperature, the chilled water setpoint temperature, and the current fraction of the design load. In this case, the sample data files that come with this model are used. Refer to the documentation of the chiller model for more detailed information about modifying these data files.

Type 198 Proportional Boiler: The boiler is used to provide a supply of hot water to the double-effect chiller. This boiler model can operate in several control modes when calculating the outlet temperature from the boiler. In this case, the boiler capacity is set to a very large number and the boiler modulates to exactly meet the hot-water

temperature setpoint; operating in internal control mode. The boiler control signal is set to 1, allowing the machine to operate whenever the inlet hot water temperature falls below the set point temperature. This input could also have been connected to the last output of the thermostat model.

Type 149 Hot Water Pump: The constant-speed, hot water pump supplies the double-effect base load chiller with a constant supply of hot water. The pump is set to be on constantly during the simulation, but could have been controlled by the last output of the thermostat model or by a simple equation that initiates the pump whenever the cooling load is positive. The one item to remember when using the pump model is that the pump sets the flow for the entire fluid loop by multiplying the rated flow rate (a parameter) by the on/off pump control signal (an input). The flow rate into this model is just used for convergence checking.

Type 278 Single-Effect, Direct-Fired Absorption Chiller: The peaking chiller in this simulation is a single-effect, direct-fired absorption chiller. This chiller is controlled to operate whenever the base-load chiller is unable to meet the cooling load of the building and the return water temperature begins to rise. Single effect chillers are not particularly efficient (COP <1); hence the choice of the double-effect model as the base load chiller and the single-effect machine as the peak load chiller. The direct-fired version of an absorption chiller uses a combustion process to provide the heat required by the chiller to cool a chilled water stream. The energy supplied by the combustion process, plus the energy removed from the chilled water stream are rejected to a cooling water stream. In most simulations, the cooling water stream rejects its energy to the ambient by the use of a cooling tower. However, in order to make this simulation easier to understand, the cooling water inlet temperature and flow rate to the chiller are assumed to be constant; taking their initial value of the inputs for the duration of the simulation. A simple addition of a cooling tower model and cooling water pump (controlled to operate when the chiller is operating) would make this simulation more realistic. The chiller modulates to meet the cooling load; attempting to cool the chilled water stream to the userdefined setpoint temperature given the available capacity. The capacity of the machine, along with the efficiency of the machine, are read from supplied data files containing the manufacturers catalog data as a function of the entering cooling water temperature, the chilled water setpoint temperature, and the current fraction of the design load. In this case, the sample data files that come with this model are used. Refer to the documentation of the chiller model for more detailed information about modifying these data files. The model calculates the amount of combustion energy required to operate the chiller and outputs this quantity.

Type 65 Online Plotters: Two online plotter models show the results on the screen from the week-long simulation. The first plot (“Loads” tab) shows the status of the two absorption chillers and the load imposed on the chillers. The second plot (“System” tab) shows the temperatures exiting the various components that comprise the chilled water distribution system. The variables are described below:

“Loads” Tab: On/Off-2E On/Off-1E Load “System” Tab: Thwo_2E Tboiler Thwpump Tchwo_2E Tchwo_1E Tpipe Tchw_ret Thwpump The temperature of the hot water stream at the exit of the double-effect absorption chiller (C). The temperature of the hot water stream at the exit of the boiler (C). A horizontal line at the boiler setpoint temperature implies that the boiler was able to meet the heating requirements. The temperature of the hot water stream at the exit of the hot water pump (C). The temperature of the chilled water stream at the exit of the double-effect, base-load absorption chiller (C). A horizontal line at the chilled water setpoint temperature implies that the chiller was able to meet the cooling load. The temperature of the chilled water stream at the exit of the single-effect absorption chiller (C). A horizontal line at the chilled water setpoint temperature implies that the chiller was able to meet the remaining cooling load. The temperature of the chilled water stream at the exit of the pipe and before the building loads are imposed (C). The temperature of the chilled water stream after the building loads have been imposed on the system (the chilled water return temperature from the building). The temperature of the chilled water stream at the exit of the chilled water pump (C). The operating status of the base-load, double-effect absorption chiller (1=On, 0=Off) The operating status of the peak-load, single-effect absorption chiller (1=On, 0=Off) The load imposed on the chilled water system by the simple building model (kJ/h)

HVAC Example 2 – Single-Zone Air Source Heat Pump Analysis
Quick Overview:
Unlike the previous example that concentrated on the water side of an HVAC simulation, this example will concentrate on the air side. In this example, a thermal zone is conditioned by two inlet air streams. An air source heat pump draws zone air, heats or cools and returns the air to the zone. The other air stream into the zone consists of ambient air that exchanges energy with zone exhaust air in a heat recovery device before passing through a humidifier and being added to the space. Controllers set the ventilation period, the air source heat pump operation, and the operation of the humidifier.

Models Used:
Type 14 Forcing Function Type 65 Online Plotter (2) Type 89 TMY2 Weather Data Reader Type 102 Humidifier Type 106 Fan Type 110 5-Stage Room Thermostat Type 196 Humidistat Type 221 Building Model Type 249 Air-Source Heat Pump Type 256 Air-to-Air Heat Recovery Device

HVAC Example 3 – Bypass HX’s in a Solar Heating Application
Quick Overview:
This project illustrates the use of the bypass heat exchanger in TRNSYS. The bypass heat exchangers attempt to control the outlet fluid temperature from either the hot or cold-side fluid by bypassing part of the fluid around the heat exchanger before mixing it back in downstream of the heat exchanger. This example shows a solar liquid heating system which is used to charge a storage tank with hot water for a domestic hot water application. The system is designed to run constantly in Albuquerque, New Mexico during the winter – a period of excellent solar radiation but with very cold nights. The first bypass heat exchanger is used to insure that the fluid entering the storage tank remains below a user-specified limit to avoid scalding problems (limiting of the cold-side outlet temperature). The second bypass heat exchanger is used to insure that the fluid returning to the collector is warm enough to avoid freezing of the fluid in the collector (keeping the cold side outlet above some minimum temperature); a boiler provides the required energy. The third bypass heat exchanger is used to keep the fluid temperature returning to the collectors below some safety limit to avoid boiling of the collector fluid (limiting the hot-side outlet temperature). An unlimited supply of mains water is available for the safety heat exchanger.

Models Used:
Type 1 Solar Collector Type 2 Differential Controller Type 4 Storage Tank Type 14 Forcing Function Type 16 Radiation Processor Type 65 Online Plotter (2) Type 89 TMY2 Weather Data Reader Type 121 Bypass HX (Hot-Side Limiting) Type 140 Bypass HX (Cold-Side Minimum) Type 149 Constant Speed Pump (3) Type 192 Bypass HX (Cold-Side Limiting) Type 198 Proportional Boiler

HVAC Example 4 – Chilled Water Storage
Quick Overview:
This example demonstrates the use of the air-cooled and water-cooled chillers in a chilled water storage simulation. In this simulation, the water-cooled chiller acts as the base-load chiller while the air-cooled chiller acts as the peak-load chiller. The loads imposed on the chilled water storage are based on a simple load equation and not on a detailed building model. The chillers charge a large chilled water storage tank by adding chilled water into the bottom of the storage tank and removing warmer water from the top of the tank. The load flow is drawn from the bottom of the storage tank, heated from the building cooling load, and then returned to the top of the storage tank.

Models Used:
Type 4 Storage Tank Type 65 Online Plotter (2) Type 112 100-Port Flow Diverter Type 114 100-Port Flow Mixer Type 149 Constant Speed Pump (3) Type 152 Air-Cooled Chiller Type 255 Water-Cooled Chiller Type 260 Aquastat (Cooling Mode)

HVAC Example 5 – Controller Demonstration
Quick Overview:
This project demonstrates the differences between the four new controllers added to TRNSYS 15.2 when driven with the same input control signal. This example is intended to make it easier for the simulator to choose which controller is the most appropriate one for the intended application. The input signal to each of the controllers is a sine wave. Separate online plots show the results from each of the controllers so that a simple comparison can be made.

Models Used:
Type 65 Online Plotter (4) Type 110 5-Stage Room Thermostat Type 258 Proportional Controller Type 261 N-Stage Heating Thermostat Type 262 N-Stage Cooling Thermostat

HVAC Example 6 – Simple Multi-Zone Buildings
Quick Overview:
This example demonstrates two uses of the simple lumped-capacitance multi-zone building model. In the first thermal zone, the zone is conditioned using the ideal internal equipment inside of the building model; effectively operating in energy-rate control by calculating the loads required to keep the building at its setpoint. In the second thermal zone the building is controlled by a thermostat which turns on and off a slab floor heating system. The two zones interact thermally via conduction through an adjacent wall and by a convective air exchange between the zones.

Models Used:
Type 65 Online Plotter Type 89 TMY2 Weather Data Reader Type 110 5-Stage Room Thermostat Type 148 Simple Floor Heating System Type 149 Constant Speed Pump Type 198 Proportional Boiler Type 221 Lumped-Capacitance Multi-Zone Building Model (2)

HVAC Example 7 – Typical U.S. Residential Heating and Cooling
Quick Overview:
This example demonstrates a very common U.S. residential heating and cooling system. The house is controlled by a thermostat that sends a control signal to the furnace in heating mode or to a central air conditioner in cooling mode. The thermostat also controls the operation of a two-speed fan; sending higher flow rates during peak heating and cooling conditions. A 2-dimensional bin sorter provides a graphical example of the weather conditions in the location selected.

Models Used:
Type 65 Online Plotter Type 88 Lumped-Capacitance Single-Zone Building Model Type 89 TMY2 Weather Data Reader Type 107 Furnace Type 108 2-Speed Fan/Blower Type 110 5-Stage Room Thermostat Type 134 Residential Cooling Coil

HVAC Example 8 – Unitary Heating Devices
Quick Overview:
This project illustrates two different unitary heating devices for TRNSYS; the heating and ventilating unit and the unit heater. These two devices combine a variable (or constant) speed fan with a heating element for conditioning of the room air. The heating and ventilating unit adds an outside air damper for mixing of the return air with the ambient air before the air passes across the heating element. In this example, two adjacent thermal zones (represented by two instances of the lumped-capacitance multi-zone building model) are each controlled by a separate thermostat which calls for heating when the room temperature dips below its setpoint.

Models Used:
Type 65 Online Plotter Type 89 TMY2 Weather Data Reader Type 110 5-Stage Room Thermostat Type 221 Lumped-Capacitance Multi-Zone Building Model (2) Type 240 Delayed Input Controller Type 247 Electric Unit Heater Type 248 Heating and Ventilating Unit

HVAC Example 9 – Hydronic Heating System
Quick Overview:
This example models a hydronic heating system for a residential heating application. A water-to-water heat pump, using mains water as the heat source, is used to charge a thermal storage tank. Hot storage fluid is then pumped across an air-to-water heating coil that delivers the warm air to the home. The home is controlled by a proportional controller that sends output control signals to the variable speed pump and the variable speed fan. The home is subject to skin loads, infiltration loads, internal loads, and loads due to occupancy.

Models Used:
Type 4 Storage Tank Type 31 Pipe Type 65 Online Plotter (2) Type 88 Lumped-Capacitance Single-Zone Building Type 89 TMY2 Weather Data Reader Type 116 Occupancy Loads Type 139 Random Uniform Distribution Type 240 Delayed Inputs Controller Type 149 Constant Speed Pump (2) Type 172 Variable Speed Pump Type 232 Aquastat (Heating Mode) Type 246 Variable Speed Fan Type 257 Water-to-Water Heat Pump Type 258 Proportional Controller Type 259 Heating Coil




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