Scenario Four - Hydronic Heating with Packaged Cooling

The following scenario completely changes out the HVAC equipment while leaving the building envelope, and internal loads the same as the previous scenario. To begin with, the five constant volume systems are replaced with cooling only, packaged terminal units. The ventilation will come through a dedicated outdoor air system (DOAS), complete with heat recovery, cooling and variable flow control. This dedicated unit will be ducted separately from the cooling system so that the outdoor air can be delivered directly to the space. This allows the DOAS to be reduced in size by 20% to account for distribution effectiveness from ASHRAE 62-2007. At the space level, the ventilation will be controlled via dampers which are actuated through CO2
control, allowing the dedicated unit to ramp down outdoor air requirements when not required. Heating will be provided from a condensing boiler designed for a low temperature return and distributed with variable speed pumps. In the zone, radiant floor or radiant ceiling panels will provide heat efficiently and comfortably. The key building components are summarized with a prescriptive target in the table below.

Table 9: Hydronic Heating Prescriptive Summary

This particular design, while efficient, is not without its challenges in a retail scenario. Many of the challenges, as previously discussed, are related to
communication between tenants and designers; however, there are some unique difficulties related to the radiant systems:

  • The radiant floor, while efficient, is slow to react to changing conditions in the space. If a large unexpected group of people were to come into the store at the same time, the space could become uncomfortably warm as the heat from the floor dissipates. Although, the controls would tell the floor to turn off, the thermal mass of the concrete would be slow to relinquish its stored heat. Conversely, if the store was to open early, unexpectedly, without the proper controls, the floor would take some time to bring the space up to comfortable conditions.
  • The radiant floor creates definite areas that the tenant would not be allowed to dig, or fasten shelves to the floor, for fear of damaging the pipes imbedded in the concrete. In a space with high turnover, this could be a negative selling point to tenants.
  • Floor coverings would reduce the effectiveness of providing the heat to the space. Since various floor coverings would act as an insulation, more energy would be expended to maintain space conditionings.
  • The boiler would take up leasable floor space, and the packaged terminal units providing cooling, or radiant panels could take up wall space from
    product or branding.

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 ‘Hydronic Heating’ scenario are summarized along with the economics of including PV in the following table.

Table 10: Hydronic Heating Cost Summary

To ensure that 51% of the site energy use is covered by onsite generation, the ‘Hydronic Heating’ option will require 13.1 kW of roof mounted PV with 12.9 kW of parking lot mounted PV (1 unit at 12.9 kW). The area required for the ground mounted PV will take up approximately 8 parking spaces. An estimate of the layout required is presented below.

Figure 9: Hydronic Heating PV Array

Directly comparing the ‘Hydronic Heating’ option to the ‘Business as Usual’ scenario shows a very efficient option. The effects of the upgraded building on the energy end-uses can be explored in more detail with the aid of the following graphic.

Figure 10: Energy End Use 4 Business as Usual vs. Hydronic Heating

Domestic Hot Water – No change from previous scenario.

Fans - Fan power drops slightly further than in the ‘Challenge Assumptions’ scenario since the ERV has a variable speed drive, and will modulate with need.

Pumps – For the first time, pumps are added to the design. In this case, only a small amount of pumping power is required because the variable speed drives recommended with the design, when properly controlled, effectively reduce the energy use.

Space Cooling
– Cooling energy at this point is approximately the same as the ‘Challenge Assumptions’ scenario. There is a slight reduction to account for the demand control ventilation reducing the need to cool outdoor air in the peak summer months.

Space Heating - Space heating (including outdoor air heating) has been significantly reduced again. In this case, the heating reduction is due to two things. From the equipment, increased burner efficiency is obtained from changing to a 95% efficient burner. From the outdoor air side, the switch to dedicated outdoor air requires the conditioning of 20% less outdoor air. By employing demand control ventilation, this amount is reduced even further.

Miscellaneous Equipment – No change from previous scenario.

Lighting – No change from previous scenario.