Table of Contents
eQuest model of the Willett Center
eQuest Model Constructions
A free program provided by the Department of Energy called eQuest was utilized to build an accurate model of the Willett Center for purposes of evaluating energy consumption patterns and assessing certain ECMs. The model was created using the energy consumption profiles, documented patterns, systems and equipment. Furthermore, the building envelope characteristics and historical local weather data is used. This effectively allowed what-if analyses to be analyzed with various ESCO rates and billing structures by using a base CAD model drawing of the Willett Center.
Interior and Exterior Lighting
The lighting system is comprised of all the internal and external lights in the Willett Center. While many of the lights in the Willett Center are controlled manually, several areas are connected to a complex control system. Several 100 watt metal halide bulbs are used in the small ballasts outside and two 42 watt recessed can lights are in each of the vestibules. The lobby area contains a large variety of lights interspersed among the large open windows. The exhibit is equipped with 100 small 20 watt spot lights to highlight artifacts and information. There are several 100 watt incandescent bulbs that are used in the movie areas for a dimming effect. Other lights in the lobby area include several small compact fluorescent 42 watt bulbs and a four foot fixture housing two T8 bulbs. The bathrooms and locker rooms are all switch based and have T8 bulbs. A majority of the offices in the back area have occupancy sensors and are mostly four-foot T8 bulbs. The storage and collection area has 47 four-foot T8 bulbs operated by a switch. These T8 fluorescent bulbs are very efficient to use in these office and hallway settings, and only use about 32 watts of power each.
Based on our count of lights and the estimates of the daily usage for each fixture, a lighting baseline has been established. The lighting has been estimated to use a total of 41.7 MWh per year. This contributes to about 15.7 % of the total electric bill (supply only). The table below shows the quantity of each different type of bulb throughout the building. The different types listed below include metal halides (MH), compact fluorescent (CF), and incandescent (I) bulbs. The CDM70 bulb is used in the outside flood lights and inside in the square angled flood lights.
To input these lights into eQuest correctly, they had to be broken down by general zones. Each room has been accounted for and every light included. The total power drawn by the lights, listed in watts, was summed and then divided by the total area of the zone. The following chart shows the breakdown of the areas and the total power for each area. Also included is the eQuest screen that is used to enter this information in Figure 5.1.2. The light schedule, broken down by individual room assignments, has been included in Appendix 9.2. Exterior lighting is calculated in a similar way. The total power used by the outside lights was summed and then divided by the total area of the building. This value is 0.1 W/sqft and contributes a total of 4.98 MWh annually to the electricity bill. This is very close, within 2%, to our initial estimate of 5.1 MWh annually.
Domestic Hot Water
There is a 40 gallon tank in the boiler room used to heat water to a given temperature, which is currently set to 120 C, all year round. This tank feeds the bathrooms, locker rooms and the kitchen sink. The piping for this system is separate than the hot water pipes for the heating system. Usage for this system is largely controlled by the seasons. Hot summer weather draws more visitors, who use more water, which consumes more gas in heating. Colder winter days have fewer visitors, less usage, and therefore consume less gas. The figure below shows the eQuest input screen for the DHW system.
Heating Ventilation and Air Cooling (HVAC)
There are two large rooftop units designed to circulate the air throughout the building. RTU-1 is designated for the visitor services area of the building that has a flexible thermostat control, while RTU-2 services the archival storage area of the building while requires much more specific temperature and humidity conditions. Both units have economizers and supply air fans that help improve the efficiency of the units. Both currents of air are conditioned by water from the two boilers located in the boiler room. The rated capacity is in CFM and the cooling load is in tons of refrigeration.
The air is then more finely conditioned upon entering the specific room in the building by two different systems. For the exhibit and lobby area, variable air volume devices, also known as VAV units, bring the air to the final temperature before entering the room. There are 8 VAV units that range in capacity size. The rated capacity relates to the air flow rate that the unit is designed for, in CFM. The heating coil is rated in thousand Btus (kBtu). For the collections area, a humidifier conditions the air for the rooms required conditions. The humidifier has a capacity of 9000 CFM and can release 21.2 lbs of water per hour.
Two exhaust fans have been installed in the building, one in the boiler room and one in the locker rooms. The locker room fan operates almost all day long, while the fan in the boiler room operates on a much shorter schedule. Three special heating units have also been installed, one in each of the vestibules and one in the boiler room. The unit heater in the boiler room has very rarely been turned on. The cabinet heaters heat the vestibules to about 60 C during winter months. All three of these heaters are run with electric motors and hot water. There are also several baseboards that contribute to the heating of the exhibit area. These baseboards are heated using hot water.The HVAC system is entered into eQuest through several different screens. The following figures show the most important input screens. The air ventilation requirements are assigned to each zone in the first screen shot. The second shot is a section of the boiler information screen and the third is a section of the cooling system input screen.
Most of the insulation throughout the building is as constructed with the exception of the attic space above the exhibit. This insulation is a blown-in foam insulation installed after a few years of operation. The thermal boundary was moved from the ceiling space to the roof space to make it match the pressure barrier of the building. Windows and doors are thermally efficient and contribute to aesthetics, having a U-value of about 0.35. Overall, the building envelope seems to be a strong barrier to the outside environment. The perimeter walls are well insulated, having an R-value of about 26, not including siding and a layer of plywood. The interior walls are less insulated, having a total R-value of about 11. The roof of the structure has a larger insulation barrier and is rated at an R-value of 28, also not including the exterior finishes.
The Willet Center has a complicate roof structure. Most of the roof is angled, but the angles are at different elevations and different heights throughout the building. Part of the roof is flat, at the atrium, and above the offices to house the root top air conditioning units. eQuest is incapable of modeling the complicated roof.
To accommodate this, the roof structure was approximated by finding the overall air volume contained by the triangular cross sections, and modeling an equivalent volume with a rectangular flat roofed cross section. To account for the varying heights in the actual roof, separate building envelopes were constructed on top of the main envelope. The roof sections were specified to be open to below. The floor to ceiling height of the roof sections was modeled to be an equivalent volume to the space above and below the angled ceiling, while the ceiling to roof section was modeled to be equivalent to the volume between the actual ceiling and the angled roof, resulting in the Building Envelope model shown below:
This approximation was tested by comparing the energy consumption profiles on a similarly sized simple structure with an angled roof and an equivalent volume flat roof. The difference in energy consumption between the two models was less than 0.01% and the can be assumed to be sufficiently negligible for the purposes of this evaluation.
As part of the effort to accurately determine power consumption within the Willett Center, a list of miscellaneous equipment was cataloged. This equipment includes computers, printers, kitchen appliances, exhibit screens and projectors, as well as a whole range of other devices that did not fit into the main system categories. The list of miscellaneous equipment cataloged can be found in Appendix 9.3. Because of time constraints and a lack of access to accurate measuring devices, it was determined that finding the actual power consumption of the miscellaneous equipment was infeasible. Additionally, the estimated total power consumption was a very small part of the Willett Centers overall power consumption, such that any error between the estimated and actual values would be insignificant to the allowed error in the overall power consumption of the Center.
To estimate miscellaneous equipment power consumption, values for average annual power consumption in kWh for similar types of equipment was found. From this annual power consumption for the miscellaneous equipment is approximately 14.5 MWh, which is about 1.5% of the total electrical power consumption in the Willett Center.
The only miscellaneous item that uses natural gas was the Roper brand gas oven. It was assumed to use approximately 0.011 MBtuss per hour, and 2 MBtus per year. This equals about 0.2% of the total yearly gas consumption of the Willett Center, which was found to be inconsequential with regards to the overall building energy usage.
In order to justify using the eQuest program to model the Willett Center and perform the energy audit, several conditions were met. The first and most important part was to check the utility bills from the model and match them to the actual bills. This was done on an annual basis as well as a monthly basis. Matching the annual bills allowed the savings to be much more accurate when finding ECMs. The monthly bills were allowed a greater margin of error because it iss energy consumption because the actual monthly building occupancy and system usage is not exactly known. Additionally, there is not an assignable cause known, except for the summer concert spike in usage.
To help match these bills, the total building system was broken down into smaller systems. These smaller systems were analyzed and annual estimates were calculated. If several annual estimates for the smaller systems matched the system totals for the model, then the annual bills would fall into place as well. Many times changing some of the input information for one system resulted in a change in the total energy consumption of another system. This meant that the smaller systems were still part of the whole and thus needed to be related, which is exactly how a building operates. This worked as a total system check. The result was a model that had been massaged into accuracy by meeting as many conditions as possible.
The following chart shows the individual system checks as well as the annual utility bill check. Errors are calculated on the right.
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