Upgrading Spatial Cooling Systems in Multifamily Buildings

Space cooling accounts for 11% of energy consumption in New York City buildings larger than 50,000 ft2. Most of these systems are powered by electricity, but some of the larger buildings also use absorption chillers powered by natural gas or district steam. Space heating, outlets, and lighting alone consume more energy than space cooling in New York.

There is a significant opportunity to improve cooling efficiency in the multifamily residential sector, where nearly half of all buildings use inefficient air conditioning systems:

• Window type air conditioning
• wall air conditioning
• Packaged Terminal Air Conditioners (PTAC)

These three types of space cooling systems have the same disadvantage: they require openings in the building envelope, which increases heat gain during the summer and heat loss during the winter. As a result, these AC units are not only inefficient but also increase the load on space heating systems.

The New York Urban Green Council estimates that annual losses due to air leaks around these AC units range from $130 million to $180 million. Furthermore, CO2 emissions associated with this energy waste range between 375,000 and 525,000 tons per year.

Space cooling systems in office buildings are generally more efficient, as the most common technologies used are direct expansion (DX) units and electric chillers, both of which are much more efficient than window, through-wall, and PTAC-type units. .

Upgrading Spatial Cooling Systems in Single Homes

Deploying centralized space cooling systems in existing multifamily buildings can be challenging as the upgrade can be highly disruptive to tenants and the allocation of space cooling expenses also becomes more complex. The cost of running a central AC system cannot be divided equally because usage varies by tenant and the space's cooling electricity cannot be metered individually if the system distributes chilled water or cold air.

However, there are also individual space cooling systems that offer much better efficiency than window, through-wall, and PTAC-type units. Two of the most promising options are mini-split air conditioners and heat pumps.

A mini-split air conditioner gets its name from how the system is set up. An indoor evaporator unit cools indoor air and circulates it with a built-in fan, while an outdoor condenser unit rejects heat. The two components are connected only with insulated refrigerant lines, which eliminates the large opening required in older system configurations.

Mini-split heat pumps are also available, offering reversible operation to provide space cooling in summer and space heating in winter. A heat pump consolidates two pieces of equipment into one unit, making it an attractive upgrade for homes that use inefficient space heating systems, such as electric resistance heaters.

The cooling efficiency of split air conditioners and heat pumps is typically indicated by the Seasonal Energy Efficiency Index (SEER), a ratio of cooling output in British Thermal Units to electricity input in watt-hours. SEER can be compared to a car's MPG value (miles per gallon), where a higher value translates into a lower operating cost. There is also an efficiency metric called the Energy Efficiency Ratio (EER), which has the same units. The difference is that SEER considers the entire cooling season, while EER is for test conditions defined by the Air Conditioning, Heating and Refrigeration Institute (AHRI). In the case of heat pumps, there is also a Heating Seasonal Performance Factor (HSPF), which is the relationship between the heating output in British Thermal Units and the electricity input in watt-hours.

Mini-split systems have a notable efficiency advantage when compared to conventional electric heating and cooling options. Suppose a window air conditioner and resistance heater are replaced by a heat pump, with a SEER of 18 and HSPF of 9. In this case, cooling savings of 50% or more can be expected, while heating savings exceed 60%. .

Discounts for air conditioning upgrades

In addition to offering superior cooling efficiency, mini-split systems are eligible for cash rebates from the Con Edison incentive program. Discounts for mini-split air conditioners are calculated as follows:

In the case of mini-split heat pumps, the following incentives apply:

Rebates improve the financial performance of air conditioning upgrades. As the initial cost of upgrading is reduced, the return on every dollar spent increases.

Recommendations before upgrading space cooling systems

When an AC unit that goes through a wall or window is replaced with a mini-split unit that does not, the cooling load is reduced because a large gap in the building envelope is closed. The update is also a good opportunity to check for other leaks, especially around windows and doors. This increases the energy savings resulting from a space cooling upgrade, as the new unit is not only more efficient, but is also subject to a reduced load.

In homes that use incandescent lighting, it is also possible to reduce the cooling load by upgrading to LED bulbs. Consider that a 60-watt incandescent bulb can typically be replaced with a 10-watt LED bulb. If 10 of them are replaced, there will be 500 less watts of heat to deal with, equivalent to a little over 1,700 BTU per hour.

Window, through-wall and PTAC units have just one advantage in terms of performance: they provide a constant supply of fresh outside air. Mini-split units are unable to provide ventilation due to the system configuration, so it is important to verify that the existing ventilation system is sufficient after removing the previous AC unit. Ventilation systems are typically designed to be self-sufficient, but it is still recommended to obtain a professional opinion; poor ventilation leads to several health problems.

Conclusion

Window-type, through-wall, and PTAC space cooling systems are among the least efficient, but are still the most commonly used in multifamily buildings in New York. Mini-split systems can reduce cooling expenses by 50% or more, while Con Edison incentives make them more affordable. However, as with any building systems upgrade, an assessment by an engineering professional is recommended for best results. Even a high-efficiency room cooling system will perform poorly if it does not match its intended application. Ensuring new equipment is eligible for discounts is also important.