WaterHeater:Mixed
WaterHeater:Stratified
WaterHeater:Sizing
Used in:
Supply side of DHW Loops
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WaterHeater:Mixed WaterHeater:Stratified WaterHeater:Sizing
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Used in:
Supply side of DHW Loops |
Water heaters are DHW loop components and can be used for simulating many types of water heaters and storage tanks, including gas and electric residential water heaters, and a variety of large commercial water heaters. They model stand-alone operation, on- and off-cycle parasitic loads and thermal losses to the zone and instantaneous/tankless water heaters. Typical applications include domestic hot water heating, low-temperature radiant space heating, and energy storage for solar hot water systems or waste heat recovery.
Water heaters have an inlet node and outlet node on the “source side” and an inlet node and outlet node on the “use side”. The source side typically draws cold water from the tank and returns warmer water, for instance, from solar hot water systems or waste heat recovery systems. The use side typically draws hot water from the tank and returns cooler water from the cold water supply mains or from the outlet of a heating system. The distinction between source and use sides is merely a convenience for reporting. They can actually be used interchangeably.
For a water heater that is indirectly heated (e.g. with a separate boiler), the source side can be used to provide remotely heated water to the tank. The source side is configured to operate as a component on the demand side of a plant loop. The design flow rate through the source side can be set by the user or autosized. The water heater input includes an additional design parameter that describes how rapidly the tank can recover.
Water heater configuration
There are currently two types of water heater:
The 1-Mixed type simulates a well-mixed, single-node water tank. The 2-Stratified type simulates a stratified, multi-node water tank. Both water heaters can be appropriate for simulating many types of water heaters and storage tanks, including gas and electric residential water heaters, and a variety of large commercial water heaters. Both types share similar features, such as on- and off-cycle parasitic loads and thermal losses to the zone. However, each type has its advantages which may make one more appropriate than the other depending on the application.
Advantages of 1-Mixed type:
Advantages of 2-Stratified type:
The EIO file reports the industry standard ratings of Recovery Efficiency and Energy Factor for water heaters. The rating method is based on the GAMA and 10CFR430 test procedures. Under certain input parameters, the rating method will not succeed and a warning message will be generated. Problems occur when inputs do not allow the tank to recover to the setpoint temperature within the test period. This can occur if the maximum heater capacity is undersized, or if the deadband temperature difference is large enough that the first draw of the test does not trigger the heater to come on. In either case, the Recovery Efficiency test will not compute properly because recovery to the setpoint was not achieved.
Standard ratings for storage-only water tanks (Heater Maximum Capacity = 0) cannot be calculated and do not report anything in the EIO file.
The following Water heater output variables are available:
HVAC,Average,Water Heater Tank Temperature [C]
HVAC,Average,Water Heater Final Tank Temperature [C]
HVAC,Average,Water Heater Loss Rate [W]
HVAC,Sum,Water Heater Loss Energy [J]
HVAC,Average,Water Heater Use Flow Rate [kg/s]
HVAC,Average,Water Heater Use Inlet Temperature [C]
HVAC,Average,Water Heater Use Outlet Temperature [C]
HVAC,Average,Water Heater Use Rate [W]
HVAC,Sum,Water Heater Use Energy [J]
HVAC,Average,Water Heater Source Flow Rate [kg/s]
HVAC,Average,Water Heater Source Inlet Temperature [C]
HVAC,Average,Water Heater Source Outlet Temperature [C]
HVAC,Average,Water Heater Source Rate [W]
HVAC,Sum,Water Heater Source Energy [J]
HVAC,Average,Water Heater Off-Cycle Parasitic Heat Rate To Tank [W]
HVAC,Sum,Water Heater Off-Cycle Parasitic Heat Energy To Tank [J]
HVAC,Average,Water Heater On-Cycle Parasitic Heat Rate To Tank [W]
HVAC,Sum,Water Heater On-Cycle Parasitic Heat Energy To Tank [J]
HVAC,Average,Water Heater Total Demand Rate [W]
HVAC,Sum,Water Heater Total Demand Energy [J]
HVAC,Average,Water Heater Heating Rate [W]
HVAC,Sum,Water Heater Heating Energy [J]
HVAC,Average,Water Heater Unmet Demand Rate [W]
HVAC,Sum,Water Heater Unmet Demand Energy [J]
HVAC,Average,Water Heater Venting Rate [W]
HVAC,Sum,Water Heater Venting Energy [J]
HVAC,Average,Water Heater Net Heat Tranfer Rate [W]
HVAC,Sum,Water Heater Net Heat Tranfer Energy [J]
HVAC,Sum,Water Heater Cycle On Count []
HVAC,Average,Water Heater Runtime Fraction []
HVAC,Average,Water Heater Part Load Ratio []
HVAC,Average,Water Heater <Fuel Type> Consumption Rate[W]
HVAC,Sum,Water Heater <Fuel Type>Consumption [J]
HVAC,Average,Water Heater Off-Cycle Parasitic <Fuel Type> Consumption Rate[W]
HVAC,Sum,Water Heater Off-Cycle Parasitic <Fuel Type> Consumption [J]
HVAC,Average,Water Heater On-Cycle Parasitic <Fuel Type> Consumption Rate[W]
HVAC,Sum,Water Heater On-Cycle Parasitic <Fuel Type> Consumption [J]
HVAC,Average,Water Heater Water Consumption Rate [m3/s]
HVAC,Sum,Water Heater Water Consumption [m3]
The average water tank temperature.
The final water tank temperature at the end of the system timestep. If reported at the "Detailed" interval, this report variable can be used to verify an exact energy balance on the water heater. Also see the report variable: Water Heater Net Heat Transfer Energy.
The average heat loss rate due to the off- and on-cycle loss coefficients to the ambient temperature.
The heat loss energy due to the off- and on-cycle loss coefficients to the ambient temperature.
The use side mass flow rate. If stand-alone, this is the scheduled use flow rate.
The inlet temperature on the use side.
The outlet temperature on the use side.
The average heat transfer rate between the use side water and the tank water.
The heat transfer energy between the use side water and the tank water.
The source side mass flow rate. If in stand-alone operation, this is 0.
The inlet temperature on the source side.
The outlet temperature on the source side.
The average heat transfer rate between the source side water and the tank water.
The heat transfer energy between the source side water and the tank water.
The average heat gain rate to the tank water due to off-cycle parasitics.
The heat gain energy to the tank water due to off-cycle parasitics.
The average heat gain rate to the tank water due to on-cycle parasitics.
The heat gain energy to the tank water due to on-cycle parasitics.
The average heating rate demanded to maintain the setpoint temperature.
The heating energy demanded to maintain the setpoint temperature.
The average heating rate supplied by the heater element or burner.
The heating energy supplied by the heater element or burner.
The average heating rate unmet by the heater element or burner. The difference between the Total Demand Rate and the Heating Rate.
The heating energy unmet by the heater element or burner. The difference between the Total Demand Energy and the Heating Energy.
The average venting rate to keep the tank below the Maximum Temperature Limit.
The venting energy to keep the tank below the Maximum Temperature Limit.
The average net heat transfer rate when considering all losses and gains.
The net heat transfer energy when considering all losses and gains.
The number of times that the heater turned on in the time period.
The fraction of the time period that the heater was running.
The fraction of the Heater Maximum Capacity.
The average fuel consumption rate for the heater element or burner.
The fuel consumption energy for the heater element or burner.
The average fuel consumption rate for the off-cycle parasitics.
The fuel consumption energy for the off-cycle parasitics.
The average fuel consumption rate for the on-cycle parasitics.
The fuel consumption energy for the on-cycle parasitics.
The water consumption rate for the use side, if in stand-alone operation.
The water consumption for the use side, if in stand-alone operation.