FEDS can be run on a machine connected to a network. In some circumstances FEDS can even be run remotely from a network computer or file share. However, because each network is different and interference and connectivity issues are possible, for the best performance (and to lower the risk of problems) it is recommended to run FEDS from a local machine.
Sometimes when the system or software crashes, certain files are locked in the system's memory which can cause strange or unstable behavior upon restarting. If this occurs, try quitting FEDS and restarting again. When closed properly, FEDS will tidy up the system resources and work properly the next time it is run.
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.
The best way to check the accuracy of a model is to run FEDS without optimization and compare the annual consumption estimated by FEDS to actual metered data. To do this, go to "Exclude Building Sets" from the "Optimization" option on the "Simulation" screen. Make sure the "Pick Building Sets" method is selected then press the "Select All" button on the left side of the screen (under the list of building sets). After saving, go back and run FEDS. This will take from a few seconds to a couple minutes for FEDS to run the baseline load and consumption calculations for the buildings. Alternatively, running with the analysis type set to "Calibration" will accomplish the same thing. Once complete, review the *.txs report for the case and check the following data:
General case and building inputs on the first five pages (for any obvious input errors)
Energy consumption data by fuel type (page 7)
Electric peak demand value and time of occurrence (page 8)
Annual energy consumption by fuel type and end use (page 10)
Do not expect these to be identical to the metered data—this is a model representation of your buildings and even if extremely precise, will vary due to discrepancies related to actual vs. average weather, human behavior, and more. Therefore, achieving consumption values from FEDS that are within 10-15% of actual values suggests a reasonably accurate model. An experienced user who is knowledgeable about building energy systems and their interactions can successfully calibrate to a much tighter tolerance.
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 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
A useful rule of thumb is that a full FEDS optimization run will take a couple minutes per building set. However, run-time depends on a number of factors, including computing resources, processor speed, size, and complexity of the case. The more buildings, use areas, and technologies being analyzed, the longer the FEDS run will take. Additionally, the presence and number of central energy plants and thermal loops will also impact run-time.
Conversely, a calibration run of the same case and computer takes only a few seconds (with additional time to generate the reports). This is because all building sets are excluded from optimization to help focus on the baseline energy results and aid in focusing on model quality assurance and calibration processes.
Installing FEDS will require approximately 1.7 GB of hard disk space. It is also important to have enough free disk space for case files. We recommend another 10-30 MB for this depending on the number and size of site models.
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.
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.
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.
The blue arrows indicate inputs that are required for FEDS to run. If any of these cells do not have a value provided, FEDS will not be able to run and will produce an alert either upon saving a screen or updating inferences. Once a valid input value has been provided and saved, the blue arrow will disappear.
The lock symbol that appears next to many of the input cells indicates the value is inferable by FEDS and does not require an input. An open lock icon means the value is not locked and may be changed by FEDS when inferences are updated. The closed lock symbol represents inputs whose value is locked and protected from being changed when inferences are updated. A user may lock a value by either entering a value into one of these cells, or by clicking on an open lock symbol to lock the value that is currently present in the cell.
Input cells that do not have an icon next to them are for values not absolutely required for FEDS to run but are highly recommended. Values, such as the fuel price data and occupancy hours are extremely important (yet a value may not be required for each fuel or day type). Others, such as the energy consumption inputs and building/technology identifications, are not used by FEDS except for reporting and aiding the user in understanding the output.
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.
In FEDS MBtu signifies Million British Thermal Units. Throughout the program, the 'M' prefix represents million or 106 (MW, MBtu), while 'k' represents thousand or 103 (kWh, kBtu).
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.
FEDS project costing algorithms account for any materials, taxes, and labor costs applicable to a given retrofit measure. Additionally, 15% contractor overhead, 10% design cost, and 6% site level supervisory, inspection and overhead factors are applied, along with any multipliers specified on the regional costs screen under the financial options. Note that many of the cost factors reflect real regional variation, including labor rates, materials cost multipliers, and sales tax rates—with differentiation driven by the specified zip code. Each of these parameters are also able to be modified by the user, if appropriate.
The non-annual maintenance cost is used by FEDS to account for costs recurring on a non-annual basis, such as incremental equipment replacements and replacing failed lamps and ballasts. For example, the present value of the non-annual maintenance cost for lighting represents the present value of the total cost (including materials and labor) to replace the burned-out lamps and ballasts of a particular lighting technology over the course of the study period (generally 25 years).
FEDS employs the same standard life-cycle costing methodology and algorithms as the building life-cycle costing computer program developed by the National Institute of Standards and Technology.
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.
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.
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.
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 discount rate is the factor used to adjust (discount) future sums of money into the equivalent current year dollar amount. It can also be thought of as the interest rate or hurdle rate (i.e., the rate of return required by a company for it to undertake a project). FEDS uses the real discount rate, which has the effect of inflation removed. FEDS provides the current Federal real discount rate as the default, but the user may enter any discount rate appropriate for their projects. Energy service companies performing shared energy savings contracts typically require real rates of return in the neighborhood of 10 to 20%.
The global cost multiplier is an overall cost multiplier applied to the total project cost (including all materials, labor, taxes, overhead). It can be used to adjust all of the total project costs used in FEDS economic calculations. This could be used for such purposes as to account for special cost-impacting requirements of working at a facility with stringent security requirements or health and safety risks, or to assess the impact of varying costs on project economics.
On the bottom right of some input screens (windows, lighting, heating, cooling, hot water, and motors) is a check box labeled "replacement required". The purpose of this selection is to tell FEDS that this particular building component or technology must be replaced. Whether it has failed (for example, windows are broken, or the furnace has stopped working), or a replacement or upgrade is planned, checking this box will force a replacement to be evaluated and selected when the FEDS optimization analysis is run. If a replacement option is cost effective, FEDS will work as normal; however, if one is not, FEDS will still provide the recommendation even though it may not be otherwise cost effective. FEDS will still report the most cost-effective option and all of the standard details to help users make informed decisions. This option is also known as replace on failure economics.
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.
FEDS project costs are based on industry averages and may not match the exact costs you will be charged. The end-use and technology multipliers are intended to enable the user to adjust for these discrepancies so that the costs used in the FEDS analyses are as close to actual as possible. The recommended approach would be to first enter any known cost data (such as, labor rates, tax rate, discount rate, etc.), and then run FEDS, generate reports, and see what types of projects are coming up. Compare the project costs to actual known costs or bids for similar projects of that type. If any of the technology costs are grossly high or low, adjust them appropriately with a technology multiplier. Rerun FEDS to see if the same technology is being selected, and make sure that the costs more closely represent what the anticipated cost to complete the project. Because of the complex nature of the FEDS cost data, this iterative multiplier approach is the best way for users to modify project costs.