Scenario Three - Challenge Assumptions

Scenario three takes the ‘Typical Upgrades’ case and shows the benefit of working with the tenant to do proper engineering calculations for sizing equipment, outdoor air and lighting levels. For equipment sizing, a software program called HAP was used to come up with a recommended unit size (see appendix). Since units do not exist in fractions of tons, the next closest piece of equipment was selected. This results in one four ton unit and four three ton units. Although sizing has been reduced from 30 tons to 16 tons, an even larger reduction in size could be accomplished by combining units. Since, for the purposes of this study, the number of thermal zones remains constant between scenarios, some of the units remain oversized. With the ability to combine zones and re(organize, it would be possible to get as low as 11 tons, or 545 ft² per ton. The key building components are summarized with a prescriptive target in the table below.

Table 7: 4 Challenge Assumptions Prescriptive Summary

Assuming an average utility rate of $0.10/kWh for electricity, $0.25/m³ for natural gas, and $0.004/ekWh for purchased offset, the estimated utility costs for the ‘Challenge Assumptions’ building are summarized along with the economics of including PV in the following table.

Table 8: Challenge Assumptions Cost Summary

To ensure that 51% of the site energy use is covered by onsite generation, the ‘Challenge Assumptions’ case will require 13.3 kW of roof mounted PV with 38.7 kW of parking lot mounted PV (3 units at 12.9 kW each). The area required for the ground mounted PV will take up approximately 24 parking spaces. An estimate of the layout required is presented below.

Figure 7: 4 Challenge Assumptions PV Array

Directly comparing the ‘Challenge Assumptions’ scenario to the ‘Business as Usual’ scenario, the effects of the upgraded building components can be explored in more detail with the aid of the following graphic.

Figure 8: 4 Energy End Use 4 Business as Usual vs. Challenge Assumptions

Domestic Hot Water – No change from previous scenario.

Fans - Fan power drops even further than in the ‘Typical Upgrades’ scenario because both the ERV and the rooftop units have been reduced in size. This results in smaller flow requirements to meet the heating and cooling set points, and a reduction in the amount of outdoor air brought into the building. The product of reduced airflow is reduced fan size in the units and power consumption in the building.

Space Cooling
- Cooling energy sees a larger decrease than the previous scenario, at approximately 60%. Again, this is due to a number of factors, including the reduction in outdoor air, the increase in efficiency in the smaller rooftop units and the reduction in fan power and lighting, which previously had been producing a cooling load.

Space Heating - Space heating (including outdoor air heating) still has a very large absolute drop in energy (60%); however, this scenario actually uses more heating than the previous. This is attributed to the reduction in lighting and fan power. With both of these end uses significantly lower, the heating system must make up for the loss of the waste heating that was previously provided through the fans and lighting.

Miscellaneous Equipment – No change from previous scenario.

Lighting - Lighting sees a much larger drop, at approximately 66%. This is attributed to the inclusion of continuous dimming fixtures coupled with daylighting sensors (as with the previous scenario), and a general reduction in the lighting levels. Should the lighting targets seem too aggressive, consider that a retail building in which Enermodal provided electrical design, Mountain Equipment Co-op in Burlington, is currently in operation with lighting levels approximately 15% lower.