Normal/typical plug loads are accounted for (inferred) automatically within FEDS. These values can be viewed and/or changed from the miscellaneous equipment inputs in maximum detail display. The data is based on major end-use load surveys for typical plug load levels and accounts for the typical levels of equipment loads in a given use-area type. For example, for an office building this will account for typical levels of things, such as computers, printers, copiers, clocks, vending machines, coffee makers, and kitchenette equipment.
No. FEDS infers parameters based on the most likely current condition of a building and its equipment. Inferences for an 1820 vintage building will reflect the typical improvements and upgrades that have occurred over time.
During a month that has been identified as seasonally unoccupied (also referred to as non-operating), FEDS assumes zero occupancy, all lights are off (except exit signs), and the cooling system is shut down. Heating is operated at a reduced level generally for the purpose of preventing the pipes from freezing (temperature kept at low setpoint specified by the unoccupied season thermostat setting). General plug loads are assumed to be non-operational, as are most motors (although this may be overridden by specifying monthly motor load factors).
Unoccupied hours or day types of occupied months are those periods during which there is reduced occupancy of the building. These are referred to as low occupancy periods in FEDS. For a typical commercial facility this might occur during the night and on weekends. A small number of occupants might be present (though less than during normal operating hours), and all energy systems remain active although they may operate at reduced levels. The operation of HVAC, lighting, plug loads, and motors are all controlled by inputs such as thermostat setpoints (enabling temperature setback), ventilation control mode, and utilization/load factors.
Full 24-hour occupancy can be specified for any day type by entering the same start and end hours (except 0 and 2400). For unoccupied day types enter 0 for both start and end times (or leave them blank). Note: if you do not specify occupancy hours, they will remain blank and FEDS will model the buildings as though they are unoccupied (reduced occupancy). Shortcut buttons are available on the standard occupancy inputs screen to make specifying continuously occupied and unoccupied day types easier.
The inputs may be accessed within the operational and control technologies section of the ventilation inputs screen. A number of technology and control parameters are available for each. A two-position or continuously modulated damper is required for some of these options.
The air leakage into a building is determined from the inferred or user-specified infiltration rate. The infiltration rate is the amount of outside air entering the building during periods when the ventilation system is either not operating or not supplying outside air (i.e., times when building is not under a positive pressure).
If the building is newer than the rated life of the equipment in question, then the remaining life is equal to the difference of rated life and building age. If the building is older than the equipment's rated life, FEDS assumes that on average, equipment will be halfway through their life (but users can override this assumption and specify actual equipment vintage). Rated lives vary by equipment technology. Some examples of rated lives used in FEDS are:
envelope components (windows, insulation, etc.) – 40 years
lights – typically 25 years (Although the cost of replacing lamps and ballasts is figured into the analysis based on specific replacement intervals and hours of operation)
boilers – 40 years
furnaces – 20 years
chillers – 20 years
package AC units – 15 years
heat pumps – Air Source/15 years, Ground-Coupled/20 years
motors – 15 years
hot water heaters – electric, 12 years; gas, 10 years; distributed heat pump, 12 years; central heat pump, 15 years
FEDS contains a built-in database of building survey data and is able to infer a number of building parameters based on the small set of required inputs provided by the user. For example, FEDS uses information such as building type, location, floor area, and vintage to determine the most likely construction type and geometry. It uses similar information along with heating fuel type and cooling equipment, to determine the most likely heating technology and ventilation system parameters for a building. All inferences enable a user to model buildings without having intimate knowledge of the detailed engineering parameters. The resulting building prototype parameter values are statistically the most likely values based on the limited set of information provided. Of course, all inferred data may be easily overwritten by simply entering (locking) a value in the user interface screens.
FEDS draws upon a number of sources to determine inferable parameter values. Major sources include national building energy consumption surveys such as the Commercial Buildings Energy Consumption, Residential Energy Consumption Survey, large end-use studies such as the End-Use Load and Consumer Assessment Program, ASHRAE handbooks, building and equipment codes and standards, and manufacturers' data and extensive building audit and evaluation experience.
A locked value, in terms of FEDS inputs, is one that the user has entered for an inferable parameter. This indicates to the model that this is a user-entered value and should not be updated (inferred). Clicking on the lock symbol can also lock a currently inferred value. When a value is locked, the lock icon will appear as a latched or closed lock. To unlock a value, simply click the icon again, changing it to an open or unlatched lock. This value will now be inferred the next time inferences are run.
Variable occupancy is an improved approach to the seasonal occupancy option which allows users to specify that certain months are non-operating (e.g., schools may be shut down over summer break). Variable occupancy also offers greater flexibility by allowing users to specify the percent of days within specific months which follow the general occupancy and operation schedule defined in the standard occupancy inputs. One hundred percent indicates the building or use area operates all days of that type during the month according the standard schedule. Zero percent indicates the building (use area) is either non-operating (shut down) or in a low occupancy state (occupied at the low occupancy and equipment use level) for all days of that type during the month. For any value between 0% and 100%, FEDS will multiply that value by the actual number of days of that type in the month and model the resulting number of days (rounded to the nearest whole day) as operating according to the standard schedule. The remainder of the days of that type in the month will be deemed either non-operating or at low occupancy (depending on the selection of non-operating period status type). As a convention, FEDS will model the first X days in the month as occupied and operating to the standard schedule, and the remaining days of that type in the month as non-operating or at low occupancy. The variable occupancy capability provides significant modeling flexibility and is particularly useful in modeling occupancy and building operation that varies within the course of a month, such as for National Guard or Reserve buildings that may only be heavily occupied on certain weekends through much of the year.
Another option for even greater control over building and use-area operation and occupancy (for each hour of the year) is also available. Contact FEDS Support for more information if interested in using this approach.
FEDS allows a negative value for percentage of heat to the conditioned space. For example, if the equipment has a COP of 2.0 and operates with an exterior condenser, then -200 should be entered for this value and the capacity should be half the actual rated capacity. (This will result in heating an amount equivalent to 200% of the unit's consumption as being rejected outside.)
The ventilation end use inputs screen contains very basic information on the ventilation motors (total capacity and efficiency). The fan motors button simply enables a user to specify more detailed motor parameters by accessing the underlying fan motor inputs screen. From here, information, such as speed, enclosure type, voltage, vintage, and number of motors can be specified. It is important to realize that if any of this information has been entered, the fan motor inputs on the main ventilation screen will be inaccessible without first deleting the more detailed inputs.
The typical FEDS user will not have detailed information available regarding plug load levels in order to adequately model them and will need to rely on the inferred values. However, miscellaneous equipment records may be modified or added if a load is unusual or atypical of the use-area type, or has an extremely large load (or one that sees extensive use) that is above and beyond what would be considered typical. Similarly, a user may want to reduce the capacity density for some areas deemed to have a lower load density than typical for that type of space, or even delete entire records when there is no equipment in use of a given type.
No. All occupancy hours must be specified by the user. Failing to do so will indicate to the model that the building is operating in the unoccupied mode each day during the week.