Space heating represents the largest share of energy consumption in New York City buildings. Also consider that many old buildings have oversized steam boilers, which increases energy consumption. Plenty of energy can be saved with newer and more efficient heating technologies, while downsizing equipment to better match the needs of each building.
Natural gas and heating oil are the most common fuels for steam boilers, and the resulting environmental impact is significant. However, this also means that efficient heating can cut greenhouse gas emissions from buildings. In new constructions, HVAC engineers normally recommend the following options:
- Hydronic systems with hot water piping.
- Variable refrigerant flow systems (VRF).
While these heating configurations offer performance advantages over steam systems, installing them in existing buildings is challenging. The installation process may disrupt ceilings, walls and floor slabs, reaching a high cost. If a major renovation is being planned for the building in question, it provides an excellent chance to improve the heating system.
Make your building heating system more efficient.
How Heating Systems Were Designed in the Past
The oversized steam heating systems found in many old buildings are not the consequence of engineering errors. Design practices and building codes were very different in the past, leading to a higher heating output.
First of all, it is important to understand that airtight buildings are a relatively modern concept. As energy efficiency gained importance, building designers started to focus on minimizing air leaks, since they increase both heating and cooling costs. Several decades ago, building codes gave a high important to natural ventilation, allowing as much outdoor air as possible into the building.
The oversized heating systems were a direct consequence of the design conditions specified in building codes of the past:
- Providing enough heating for the coldest days of winter, considering windy conditions.
- Assuming that the windows are left open on these cold and windy days.
Old heating systems are designed for buildings that constantly receive cold winter air through their open windows. Under these conditions, their high design capacity should come as no surprise. Heating a modern building with an airtight construction and controlled ventilation requires a much smaller heat input. In fact, when a steam heating system does not have controls for individual dwellings, opening the windows often becomes necessary.
Another factor that led to oversized steam boilers was the constant change in fuels. The first boilers relied on coal, then heating oil became dominant, and natural gas is the most common fuel today. Design practices were more difficult to develop when fuel options were changing, and many boilers were oversized just to make sure they would work.
Improving the Efficiency of Steam Heating Systems
If there are no plans to replace a steam heating system, thermostatic radiator valves (TRV) can be an excellent energy efficiency measure. They limit the flow of steam into individual radiators, and the resulting energy savings can exceed 10%. Older TRVs control steam flow with a plug that expands and contracts, while newer TRVs are electronic.
Additional savings are possible by upgrading to a newer and more efficient steam boiler. Some modern units have temperature sensors and modulating burners, allowing a heating output optimization that is not possible with older units.
According to the NYC Urban Green Council, these upgrades can reduce steam heating costs by around 20%. In many cases, the upfront investment is less than $1 per square foot of building space. The potential savings are higher if the building insulation is improved, while air leaks are detected and sealed.
The NYC Green New Deal mandates a 40% reduction in city emissions by 2030. Many buildings that are heated by steam will need an upgrade to reach that goal. According to the Urban Green Council, only around 25% of buildings are compliant, and the other 75% will need upgrades.
Replacing a steam heating system completely is also possible, but the project becomes very expensive. Piping and radiators may need significant modifications to use hot water, and they are incompatible with variable refrigerant flow system. A complete heating upgrade is simpler during a major renovation, where large portions of the building are dismantled and rebuilt.