On the *.txs report, the electricity dollar values listed under the "Annual Installation Energy Use by Fuel Type" and "Annual Energy Use by Building Set and Fuel Type" pages include both energy and demand charges. To determine how much of that total cost is attributable to the energy vs. demand, the demand component (reported on the following page) may be subtracted from this total value.
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).
Emissions factors are used and relate a quantity of pollutant emitted (e.g., tons of CO2) per unit of fuel burned. There are factors for each of the six pollutant types corresponding to each main fuel type. To estimate emissions, FEDS multiplies the consumption value for each fuel type by the appropriate emission factor. The emissions factors for certain fuel types, (for example electricity) can vary significantly depending on factors, such as plant type (coal, gas, nuclear, hydropower) and source fuel composition (e.g., sulfur content) such that state average values are applied based on the typical generation resource mix supplying that state.
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.
FEDS was originally designed to model buildings with single, homogeneous heating and cooling technologies within each individual building. The portion of building set served inputs are available to specify whole buildings within a building set that are served by a given technology. If your building has more than one type of heating or cooling technology, there are a couple of options. If the majority of service is provided by one system, users might simply model that one as if it were the only system serving the building. If the occupants use portable space heaters, users could account for the energy consumed and heating service provided by representing them as a miscellaneous equipment record. If, on the other hand, one system does not dominate, it would be best to model the building as a pair of linked buildings, with one technology serving each portion. Or, if a major renovation is being contemplated, users might wish to model the building once as if it were served by one technology, and once by the other. Optimizing each case separately, the results will provide insights into which system type would be best for the building.
An option is also available that makes it possible to model multiple heating or cooling technologies serving the same building(s). To enable this feature, select the percentage of each building served option from the heating or cooling end use inputs. When this option is specified, FEDS will model the defined HVAC technologies as serving the specified portion served of each building in the building set.
If the boiler serves only one building, select single building boiler as the equipment type and the fuel type that fires the boiler (natural gas, distillate oil, etc.). If the steam is piped in from a central boiler plant or purchased from offsite, select central steam as the fuel type and specify the equipment type as either a radiator, fan coil, or air handling unit using central steam or hot water (in-building equipment is a heat exchanger). For steam purchased from an off-site supplier, input a price for purchased central steam in the non-electric energy price inputs. For self-generated steam, create a central plant record, associated conversion equipment, and thermal loops within the central plant and thermal loops inputs.
inking two distinct building sets together allows greater flexibility in modeling complex building geometries or uses. Linked buildings are designed to model two buildings that share a common wall or are stacked on top of one another. Specifying that the buildings are linked directs FEDS to automatically (based on the geometry information for each building) determine the wall area (or roof/ceiling area) that is shared, and thus not exposed to exterior conditions. It essentially calculates the portion of each buildings shell that is an adiabatic surface (i.e., does not experience conductive heat transfer) and does not receive solar gains. It uses this information in load calculations to appropriately account for the impact of the buildings being connected. There are some rules, however, that must be satisfied in order to link building sets. First, both sets must contain the same number of buildings so that a direct one-to-one linking is achieved. Second, both sets must have the solar normalization turned off (calculate solar gains by facing direction). Also, FEDS currently does not model cantilevered buildings so for top/bottom linking, the N/S and E/W lengths of the top building must not be greater than the corresponding lengths of the bottom building.
The number of heat or cooling equipment should be specified. For boilers or chillers, enter the number of boilers or chillers and not the number of air handling units or fan coil units. Similarly, for furnaces, packaged cooling units, and heat pumps specify the number of those devices. If the building is served by a fuel generated at a central plant (not within the building), specify the number of heat exchangers that transfers heat from the central distribution loop to the building loop.
Attractive NPVs, payback periods, and SIRs typically fall within certain ranges, which should always be positive. However, negative values are possible in a couple of instances and do not necessarily indicate an error. The first possibility is that the project is recommended for a technology or building component you identified as "replacement required". As such, FEDS will recommend the most cost-effective replacement option, but not require that it be cost effective. So, while it may be the best replacement option, it may exhibit seemingly nonsensical economic figures of merit. Similarly, if a building retrofit occurs due to central plant or thermal loop abandonment, it may also exhibit negative savings criteria. That simply means that the retrofit (e.g., replacing central steam service with an in-building boiler) was not cost effective when looking just at the building energy use and costs. But the value of abandoning the central plant and/or distribution loop (due to the accompanying reductions in thermal losses and O&M costs) provided a net positive gain when added to the negative savings at the building level. Thus, at the site level, taking the central plant and thermal loop savings into account, the net benefit is positive—but purely from the building perspective (reflected in the TXD and CSV reports) the change from steam to dedicated boiler was not cost effective. Reviewing the central plant and thermal loops section of the TXS report and looking for a positive abandonment value will provide additional detail on just how much of a net positive gain accrues do the abandoning the plant and/or loop.
This is an error message that comes up when there are incompatible heating or cooling systems defined in a building set. This can occur when one building is modeled with linked heating (a heating system requiring a fan to deliver the heat; e.g., furnace, fan coil, or AHU) with one served by an unlinked heating system (no fan required ; e.g., radiator or baseboard system) together in the same building set. The situation can be remedied by separating the buildings into distinct building sets. For more information about allowable HVAC combinations, refer to Appendix I of the FEDS User's Guide.
Prototype buildings in FEDS are modeled as basic rectangular blocks, with the actual geometry calculated based on the total floor area, number of floors, floor-to-floor height, and aspect ratio. However, additional geometries can be modeled by using the linked building approach or through the advanced geometry inputs, which allow modification to underlying parameters including window/wall/roof/floor areas and conditioned air volumes.
The index code in following the existing technology description for a heating or cooling technology represents the technology record number. For example,{H2} indicates a heating technology is actually heating record #2 (as input in the user interface). This information can be valuable when dealing with heat/cool pairs with several heating and cooling records in a single building set.
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.
A dual-fuel heat pump is an electric air-source heat pump that uses another fuel source (natural gas, LPG, oil) for the auxiliary or backup heat (instead of electric resistance coils). It can be accomplished within a single integrated unit or pieced together by mating a standard air source heat pump with a furnace via a controller. The controller determines which unit to operate based on outside temperature, relative efficiencies, and cost of each fuel.
The heat/cool pair is a concept added to FEDS with the advent of considering heat pumps as replacements to conventional heating and cooling technologies. A heat/cool pair identifies to the model which heating and cooling technologies jointly serve a particular building or group of buildings in the building set and may be considered for joint replacement by a heat pump technology. In order to consider heat pumps or any other integrated heating and cooling technology as replacements for existing heating and cooling technologies, the heat/cool pairs must be defined. Baseline heat pump records are automatically paired (as long as their fuel type, equipment type, number of units, and vintages match) upon updating inferences, while all non-heat pump technologies must be paired manually.
The advanced geometry inputs allow for more flexibility in modeling non-standard building geometries compared to the linked building approach. When accessing the advanced geometry inputs, the user may specify or alter a number of geometric parameters for each zone of the building to customize the resulting model. For example, the exterior wall areas and window areas can be specified for the north, east, south, and west sides of each zone. Additionally, roof, floor, footprint areas, exterior perimeter length, and conditioned air volume can be specified for each zone. These adjustments provide users with the ability to model a number of more complex geometries, such as individual parts of a strip mall complex or varying window fractions for different sides of a building, with greater accuracy than through other means. The option can be accessed via the button on the regular geometry inputs screen.
A linked heating and cooling system is when the heating and/or cooling coil is integrated with the ventilation system, employing air as the distribution fluid (air handler, fan coil, packaged unit, furnace, etc.).
An unlinked heating and cooling system is when the ventilation system (if present) is separate from the heating coil, and heat is provided without requiring fan-powered air delivery. Unlinked heating technologies include radiators, baseboard electric, or infrared heaters.
Currently, FEDS assumes that all cooling is linked, with the exception of evaporative coolers, which are assigned a separate, special ventilation scenario. For more detailed information see Section 4.4.2 of the FEDS User's Guide.
Solar normalization is used when the orientation of a single building is unknown, does not align with N/S/E/W directions, or when there are multiple buildings of differing orientations in a building set. It can be used to avoid biasing the solar gains calculation by normalizing the exterior wall, window, and roof areas, such that the resultant loads are roughly the average of two buildings: one with an east/west orientation and one with a north/south orientation. FEDS can be set to "ignore facing directions" to use solar normalization.
The aspect ratio is used to define the geometric orientation of the buildings in a building set. It is a ratio of length to width and is calculated by dividing the typical north-facing length by the typical east-facing length.
The crossover temperature is the outdoor air temperature at which a dual-fuel heat pump switches operation from the heat pump to the backup technology. This is typically the control methodology for these systems and can be entered or determined by FEDS. FEDS will calculate the optimal crossover temperature based on electric and backup fuel prices, heat pump performance and capacity vs. temperature, and furnace efficiency.
Section 432 of the Energy Independence and Security Act of 2007 (EISA 432) requires U.S. federal agencies to perform energy and water evaluations of their covered facilities on a recurring basis and report their performance via the Compliance Tracking System (CTS). The FEDS CTS report is provided to help agencies compile and format results from their FEDS analyses to facilitate this reporting requirement. Measures identified with buildings modeled in FEDS are categorized and summarized into the CTS Evaluation Upload Template (in an Excel spreadsheet format).
A separate heat/cool pair is a pair of heating and cooling technologies that are completely separate units, yet serve the same area/building (e.g., a furnace and separate package unit, or a boiler and a chiller). An integrated heat/cool pair is one in which the heating and cooling sources are packaged together in the same unit (e.g., a packaged cooling unit with integral gas burner or 'gas-pack' system). Identifying a heat/cool pair as integrated tells FEDS that individual heating and cooling replacements cannot be considered as a direct replacement.
Similar to the separate vs. integrated discussion for heat/cool pairs, a separate backup source for a dual-fuel heat pump indicates there is a separate furnace that is connected to the heat pump via a controller. A dual-fuel heat pump with integrated backup is a heat pump unit with a built-in gas or LPG auxiliary heat source. For modeling purposes, the only real difference is that FEDS will consider replacing the individual components (heat pump or backup furnace) of a separate dual-fuel heat pump in addition to replacing the entire system.
The Energy Resilience and Conservation Investment Program (ERCIP) report (*.ecp, otherwise known as the DD 1391) is a special form required by certain U.S. Department of Defense agencies in order to submit projects for ERCIP funding. The ERCIP report is designed to facilitate the form preparation and submittal process.
The [Heating/Cooling] end use designation is used for existing heat pumps or heat/cool pairs. Because such technologies provide both heating and cooling, two rows are needed to describe them on the *.csv report. [HEATING/Cooling] indicates that the data on that row pertain to the heating technology (and overall economic impacts) while [Heating/COOLING] indicates that the data describes the cooling portion of the equipment (and no overall energy and economic data are shown).
Thermostat dead band for heating represents the range of temperatures below the set point at which the thermostat does not call for heat. For example, at a 70-degree set point and a 2-degree dead band, the temperature will drop to 68 degrees before heating is activated, raising the temperature back to 70. It may also be referred to as the throttling range or differential. It operates similarly for cooling, allowing the temperature to rise a number of degrees equal to the dead band before cooling is activated.
For heat/cool pairs (separate heating and cooling technologies), information may be listed for both retrofits to new, more efficient equipment and to a heat pump. In some cases, it may be cost effective to replace the heating equipment (or cooling only, or both) with a newer unit of similar type, as well as replace both heat and cool simultaneously with a heat pump system. All cost-effective options will appear on the *.csv report. The best option can be determined by comparing the sum of the individual heat and cool annualized total life-cycle costing savings with that of the combined heat/cool system (i.e., heat pump).
The installed capital cost listed at the very bottom of the *.txd report represents the actual total cost including materials, labor, taxes, and overhead. It is the actual cost that would be paid to complete a project. The installed cost value listed under the life-cycle costs savings section displays both the present and annualized values of the installed cost as used in the life-cycle cost analysis. The present value of the installed cost may be less than the installed capital cost if the study period for the analysis is less than the life of the new equipment. This can occur when the remaining life of the existing technology is less than the life of the retrofit technology. In this case, the cost of the retrofit technology is annualized over its full rated life, but only the annualized costs occurring during the remaining life of the existing equipment is discounted back to the analysis year and used for a fair cost/benefit comparison.
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.