Before the renovation, Castle Square had four boiler rooms, each serving 48 apartments with hydronic baseboard heat and hot water. Residents did not pay for heat and hot water. Before the renovation, each apartment had its own through-the-wall air conditioner. Residents did pay for air conditioning.
During the design process, the team explored the idea of providing each apartment with its own heating and cooling equipment. The idea was that if residents pay for heat and cooling, residents would use less energy. The team also hoped that they could eliminate the through-wall air conditioners, which create heat and cooling loss, because they are a big gaping hole in the building’s facade.
In the end, giving each apartment an individual boiler or furnace would not technically work, because each apartment’s heating requirements were so low (due to super insulation) that no manufacturer actually makes a boiler or a furnace small enough!
The team also considered using individual air-to-air electric heat pumps at each apartment for heating and cooling. The benefit of heat pumps is that they can be sized small enough to meet the heating and cooling requirements of each apartment. They are also about 2.5 times more efficient than electric heat and cooling.
However, the team opted against the air-to-air heat pumps, because they were concerned that submetering technology was not reliable enough to bill residents individually for their heating and cooling costs. The team predicted that residents may use more cooling than necessary, if they weren’t paying for it. On the heating side, the team was also concerned with the higher carbon footprint of using electricity for heating (as opposed to natural gas).
Given these issues, the team was comfortable with keeping the central boiler room configuration. However, they really struggled with the idea of keeping the through the wall air conditioners. Through wall air conditioners seem counter intuitive, because they create a big hole in the super insulated shell. The team looked at other air conditioner options, but they couldn’t find one that satisfied both requirements – 1) no big hole in the shell and 2) residents still pay for air conditioning.
After much deliberation, the team decided to keep the central boiler rooms and go with Energy Star through-wall individual air conditioner units. Yes, the air conditioners are a compromise. The big hole and the associated air conditioner add a 3 percent increase in heating/cooling requirements. However, in the end, the team decided to make this choice, because they felt that “free” central air conditioning (which is also a lot more expensive to install) would lead to overuse by residents, offsetting any savings that would have been gained from avoiding the air conditioning sleeve wall penetration.