Space heating, water heating and power reliability are critical to multifamily building operations. With combined heat and power (CHP), you can get all three — and energy savings to boot. More than 400 CHP systems have been installed in multifamily complexes in the U.S. since 1987. These innovative facilities realize the many benefits that CHP systems have to offer multifamily buildings.
How CHP systems work
A CHP system typically consists of an internal combustion engine that drives an electric generator. Waste heat is captured through various heat exchangers, including the oil cooler, engine jacket and exhaust manifold, and then used to heat hot water. There are no electrical transmission losses, and it can help reduce demand charges. CHP units use up to 85% of the fuel burned, according to system suppliers. This compares to an average fuel source efficiency of 33% for grid-supplied power.
Most CHP systems for multifamily buildings use natural gas-fueled reciprocating engines with an average power output of 80 kilowatts (kW). However, these systems can range up to 1 megawatt (MW) in output. Some systems use gas turbines averaging about 120 kW in output. Micro-CHP systems produce less than 50 kW of electricity, but can be paralleled together to achieve higher system output.
CHP in multifamily buildings
Multifamily buildings with the following attributes are good candidates for CHP:
- A single building with 100 or more units.
- A central domestic hot water system.
- A year-round need for hot water.
- A spark spread » $12 per million Btu (MMBtu).
The spark spread is basically a comparison of the purchase price of utility electricity compared to the cost to generate it onsite using natural gas.
CHP success stories
How does CHP work in the real world? Let’s look at some examples.
The Eltona in New York City is a five-story 72,000 apartment complex. The building uses two micro-CHP units that each produce 4.4 kW of electricity and 39,000 Btu per hour of heat. The system provides 87% of electricity demand in common areas and 25% of the heating needs for the entire building. The system also eliminates four tons of carbon dioxide emissions a year, which helped the building achieve LEED Platinum green building certification.
University Square Apartments in Philadelphia is comprised of 442 apartments. They installed two 75 kW packaged CHP systems that run 20 hours a day. The system provides 16% of the building’s electrical load and 34% of total space heating and hot water needs. The $500,000 installed cost was offset by a 50% grant from the state of Pennsylvania. The system reduced annual carbon dioxide emissions by 550 tons.
If you’re looking to save energy, improve power reliability and reduce emissions in your multifamily building, consider combined heat and power.