In the ‘Enter Building Details’ module, you defined the source of heating for both air-handlers and at the zone level. In the event that boilers were chosen for either of those, tThe boiler type (condensing/non-condensing) and the boiler sizing (in order of priority of operation) are required for this step. Note that most identical boilers in a system are likely to rotate in terms of which one is the lead boiler, and that is okay. A smaller or larger boiler, compared to the rest of the boilers in a system, is likely to be a dedicated lead or lag boiler and should be specified in the priority order accordingly. Boiler efficiency is an optional input. The default is 80% for non-condensing boilers and 91% for condensing boilers. Boiler stage-up part-load ratios are also optional as input. The default is 100% loading to sequence the next boiler. There is no benefit to under 100% for non-condensing boilers.
For the hot water loop, there are four parameters to define:
- The Design Coil Waterside Delta-T: If known, this is a property of the hot water coils that is used to aid in sizing hot water pump design sizing. A good default is 20°F.
- Line Losses to Unconditioned Spaces: This field helps to account for thermal losses in piping, valves, and other hot water system components that do not provide a productive source of heating to the building. These would include spaces like mechanical rooms, plenums, chases, above-ceiling spaces and other areas that are normally unconditioned. Four qualitative options (zero, low, medium, and high) are provided, which correspond to quantitative values in the model. An intuitive answer can be provided by the user based on any known characteristics of the hot water loop and its insulation. If zero is chosen, there will be no benefit from any measure that adjusts the temperature of the hot water loop for non-condensing boilers.
- Design Loop Differential Pressure: If known, this is the pressure required to deliver full hot water flow to zone-level heating coils. If the pressure setpoint is currently constant and this value is unknown, it is recommended to use the current constant differential pressure for this parameter. If unknown, 15 psi is a good default.
- Plant Side Simultaneous Heating and Cooling: This parameter will mix heating and cooling between the hot water and the chilled water loop during times that both loops are actively running (building loop pumps are on). This might be the case if significant amounts of uninsulated piping or loop components are present in the same areas of the building, or if zone level equipment (e.g. 4-pipe fan coil units) have valve leaks or other issues that cause both heating and cooling to flow at the same time. The magnitude of the issue can be identified qualitatively here. For most buildings, this will not be a problem, and zero is a good choice.