Understanding loads for ApacheHVAC components in Vista Results
It’s important to understand what you’re looking at when viewing loads for ApacheHVAC components within Vista Results view. The following is meant to touch on just a few points that may be less obvious in terms of how the numbers you see in the results relate to the capacity of the components and the loads that they convey to heating and cooling plant equipment.
Coils are relatively more straightforward in that their capacity or loading is a function of design inputs:
- For simple coils, the capacity set in the coil dialog will be the capacity, regardless of conditions on either the air or water side of the coil. This load will be passed to the connected water loop or directly to the heating or cooling source if no water loop is present.
- For advanced coils, the capacity of the coil is a function of the relationship between the design conditions and the actual conditions at any given time step as well as the temperature and flow rate of the connected water loop.
Water loops will contribute to the load seen by a boiler or chiller: heat rejected to the water loop by pumps will add to or subtract from the load placed upon the loop by coils and other devices.
Room units, unlike coils, have heating and cooling effects associated with the presence of their mass within the conditioned space: Regardless of whether it is OFF (i.e., not active or presently engaged) or ON, the thermal mass of any room unit will play a role in adding heat to or removing heat from the space. All room units will thus have a load profile differing at least somewhat from the load profile seen by the heating or cooling source to which they are coupled.
For example, a radiator will heat a room less as its mass is warming up and will continue to heat the room after the flow of hot water to it is turned off. And, even if it never turns on, a radiator will absorb a minor cooling load while sitting idle in a space as the space grows warmer. Thus at the end of a hot summer day when the air conditioning runs just to closing time, a radiator will contribute ApHVAC Room Unit Cooling Load (via stored “coolth”) when the airside AC system shuts down and the room begins to grow warmer.