Heating/Cooling Choices

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.

AFTER - The Castle Square team decided to stick with the central boiler room configuration (4 boiler rooms each serve 48 apartments). This photo shows one of the tiny boilers that replaced the existing central boilers. There are only 3 of these tiny boilers in each boiler room. The boiler can be so tiny, because the super insulation drastically reduced the heating needs of the building. One of the benefits of sticking to a central heating system is that the boilers could actually be sized to match the tiny heating loads of the apartments. In contrast, if we wanted to provide each apartment with its own boiler, that boiler would have been drastically oversized - they don't make boilers small enough to match the teeny tiny heating load of each super insulated apartment!

BEFORE – The enormous 70 percent efficiency atmospheric boilers are being replaced at Castle Square.

BEFORE - Before the renovation, Castle Square residents paid for their own air conditioning and had through-the-wall air conditioners.

AFTER - One of the biggest compromises that the Castle Square team made was to keep the through-wall air conditioners. Although the existing air conditioners will be replaced with high efficiency air conditioners with minimal air leakage, they still cause a 3 percent heating and cooling loss because of the hole they create in the building's insulated shell. The benefit of keeping the air conditioners was was that residents will continue to pay for their own air conditioning and will hopefully keep usage down.

Air-to-air heat pumps, like the one shown above, were one of the heating and cooling options considered at Castle Square. In the end, the team decided against using them.

This is a condensing unit for an air-to-air heat pump. The design team chose not to use air-to-air heat pumps at Castle Square, because they are difficult to submeter. As a result, the team was not confident that they could bill residents for their heating and cooling usage.