Prices must be provided for all fuels being used in the buildings being modeled. In addition, prices may also be provided for fuels not currently being used for FEDS to consider those fuels in its economic calculations (e.g., to consider fuel-switching opportunities).
TIP—Watch units required for fuel price parameters! Electric energy prices are requested in ¢/kWh, while demand charges are in $/kW.
Generally, it is best to specify the original purpose of the building as the building type, and then modify the use-area type to reflect its current use. Select building type = "Education", use-area type = "Office." The building's construction characteristics are inferred based on building type, while usage parameters (including occupancy, lighting and equipment use, and hot water demand) are based on the use-area type.
There is effectively no limit to the number of building sets allowed in a single case if there is enough hard drive space. Currently, each building set occupies approximately 4.3 megabytes of space across all file types. Given adequate storage space, FEDS can be—and has been—used to model an entire community, city, or utility service area.
There is no real limit to the number of buildings that can be modeled in a building set. However, building sets are designed to model buildings that share similar characteristics. The more similar buildings are within a given building set, the more accurate the results will be.
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.
Use the building type or use-area designation that best fits regardless of which list it is on. The building set classes were grouped this way to aid in the selection of common types, but either list may be selected.
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.
Typically, the "Other" fuel type represents liquid propane gas (LPG) or propane fuel. However, if you use another fuel type that is not listed (e.g., wood chips), you may use "Other" to represent this fuel type.
A minimum or contract demand is included in some commercial and industrial electricity tariffs. It specifies the minimum billing demand that will be charged each month. This is important to understand because implementing energy efficiency projects that reduce the site’s monthly peak demand below the contract demand will have limited return, as no additional savings in demand charges will accrue once the actual monthly demand falls below the minimum contract value. If that is possible for your site, it is best to review this with your utility and negotiate a lower contract demand.
A demand ratchet is a billing method commonly imposed by electric utilities on large commercial or industrial customers. It specifies that the billed demand level in kW be the larger of the actual peak demand for the billing period, or a percentage of the highest peak reached during the previous X months. A typical demand ratchet uses 80% of the peak demand occurring during the previous 11 months as the comparison point. Under this scenario, if your facility experiences a peak demand of 1,000 kW for one hour (or 15 minute interval) you will be billed for a minimum of 800 kW during the next 11 months, even if your actual demand is much lower. Demand ratchets are generally used by utilities to reduce the risks of serving certain types of customers who have potentially large swings in demand during the year—making them pay for the assurance of having the high capacity available when needed.
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 marginal price is the price paid for the last increment of energy purchased. This should, therefore, exclude all fixed charges (e.g., the monthly customer or meter charge) and focus only on the costs that vary based on the amount of energy used. Some rate structures are more complex and require some analysis. For example, in a block electric rate structure where users pay a certain amount depending on how much electricity used during the month, the value of electricity would be the price corresponding to the amount the building generally consumes in a month (rather than the average cost over all kWh's used). The marginal rate is the value of a unit of energy saved (i.e., the value of a kWh saved by an efficiency measure).
Providing detailed marginal prices for electricity (including any time-of-day or seasonal variations, and the impact of demand charges and ratchets) is important as it can have a huge impact on the types and cost effectiveness of recommended efficiency measures, as compared with applying basic melded average rates.
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.
Distillate oil is light fuel oil that has been further refined than heavier oils. Examples include #2 fuel oil and diesel fuel. Residual oil, as its name suggests, is the oil residue that remains after distilling out the lighter grade components. It is generally designated as #4, #5, or #6 fuel oil, is much more viscous than ordinary oils, and must be heated to allow it to flow and be burned.
Most fuels are valued in FEDS as delivered to the building or end-use. However, the value for district fuels at the building or end-use level are determined somewhat differently. For self-generated fuel types (e.g., central steam, hot water, or chilled water) FEDS calculates the value of the fuel from the inputs in the central plants and thermal loops module. For example, the average value of self-generated steam is calculated based on the energy price of the fuel consumed by the boiler at the central plant along with its conversion efficiency, value of auxiliary energy and chemicals and labor to operate the plant, plus thermal and leakage losses in the thermal loops that distribute the steam to the building. If the central steam plant has multiple distribution loops, the losses may be different and therefore each steam loop can have its own average value for the steam it delivers. For purchased central fuel types (purchased steam, hot water, or chilled water) the value of the fuel delivered to the installation boundary is entered on the "Non-Electric Energy Prices" screen, and then FEDS applies information on the efficiency of each distribution loop to determine the average value of the steam at the building level as delivered by each loop. Marginal values do not consider fixed O&M costs (i.e., those that do not vary with the quantity of central fuel produced/delivered) or distribution losses (which are fixed and do not vary with the amount of energy delivered). Marginal values are used to determine the value of each increment of energy consumed or saved.
No. Given the importance of energy prices on the analysis, as well as the significant variation in rates available within a given region, there are no default or inferred electric or non-electric fuel price data. Users should enter the value of all fuels available.