Space heating represents the highest energy use in New York City buildings. In addition, domestic hot water and space cooling systems use less energy than space heating, but they are also among the top five building systems that use the most energy. As a result, a building can reduce its energy consumption dramatically by replacing its existing heating and cooling systems with modern and high-efficiency equipment.
However, before proceeding with a large-scale building upgrade it is necessary to define a starting point. Building upgrades are investments after all, where the property owner spends capital with the goal of achieving a permanent reduction in building ownership cost. In other words, building system upgrades only make sense from the financial standpoint if the long-term benefit outweighs the associated upfront expenses.
Is There an Upcoming Major Renovation?
Heating and cooling upgrades provide long-term benefits but can be disrupting for building operation. If a major renovation is planned in the short term, it represents an excellent chance to also improve HVAC performance.
A major renovation also provides an excellent chance to improve the building envelope. Poor insulation and air leaks can be detected and fixed, reducing the required heating and cooling capacity after the renovation. This way, the new heating and cooling systems can be specified not only with a higher efficiency, but also with a lower capacity.
For example, if you replace a 100-ton air-cooled chiller consuming 1.2 kW/ton with a more efficient water-cooled unit that only uses 0.6 kW/ton, you achieve 50% energy savings.
However, if the new unit has a required capacity of only 80 tons thanks to building envelope improvements, energy savings are increased to 60%.
A building envelope improvement can be complemented with a lighting system upgrade. Solid-state LED lighting emits significantly less heat than incandescent, halogen or old fluorescent lighting. All this heat is subtracted from space cooling loads, providing additional energy savings beyond those achieved directly with the lighting upgrade.
Consider that a 60-watt incandescent bulb can generally be replaced with a 10-watt LED bulb, and a 4-lamp T12 fluorescent fixture (4x 34W) can generally be replaced with an integral LED fixture consuming 40-45W. The lighting heat reduction is not significant for a single fixture, but can save several tons of cooling capacity in a building with hundreds of inefficient fixtures.
Building Upgrades: Cost and Benefit
When upgrading a NYC building it can be tempting to prioritize space heating systems, since they consume the most energy. However, it is also important to consider the energy source used by each appliance.
For a given amount of energy delivered, electricity is far more expensive than gas in NYC. Natural gas from Con Edison has a price of around 1.05 USD per therm for residential users, which translates to approximately 3.6 cents per kWh of heat, before considering appliance efficiency. On the other hand, electricity prices typically exceed 20 cents per kWh. Even if most combustion appliances are less efficient than electric appliances, the price of electricity is too high compared with that of gas. This effect is evident in electric resistance heaters, which are around four times more expensive to operate than gas heaters in NYC.
Property owners can achieve the best results by getting a professional energy audit before deciding which building upgrades to carry out. With an energy audit, property owners can get a detailed breakdown of energy efficiency measures, along with the expected cost of each. More importantly, an energy audit helps determine the return on investment for each energy efficiency measure - how many dollars will it return over its service life for each dollar spent upfront? Given the price gap between electricity and gas in NYC, upgrades that target electric system generally offer a shorter payback period and a higher ROI.
Before proceeding with any building upgrade, checking the Con Edison incentive program is highly advised. Many energy efficiency measures are eligible for attractive cash rebates, which further improves their financial performance. Consider that some rebate programs only apply during certain times of the year or have limited funding, so building upgrades should be planned accordingly.
Importance of Building Type
Not all buildings consume energy the same way. For example, mechanical ventilation typically represents around 13% of energy use in office buildings, but only 1% in multifamily residential settings. This is a consequence of the requirements established by NYC construction codes for each property type - natural ventilation design is mandatory in residential constructions, but designers can choose between natural and mechanical ventilation for office buildings. Domestic hot water systems experience the opposite effect as ventilation systems, representing only 2% of energy use in office buildings but 19% in multi-family residential buildings.
Differences like this are present for many building system. For example, office occupancy is normally higher than residential occupancy during the day, which extends lighting and space cooling schedules for office buildings, and the corresponding energy expense. However, this does not mean lighting and cooling upgrades should be discarded in the residential sector: these systems represent a reduced percentage of energy consumption but are typically older than those found in office buildings, which can result in an attractive financial return.
When deciding which cooling and heating upgrades to prioritize, it is very important to select an adequate timeframe for the project, and getting an energy audit to determine the cost and benefit of each measure. Ideally, deep retrofits should be scheduled along with major renovations to minimize disruption and cost. It is also important to find synergy between upgrades, for example when both lighting and space cooling are upgraded. Of course, the financial return is also a very important consideration: as a property owner you will want to prioritize measures that maximize the return on each dollar invested.
In general, energy efficiency measures that target electric systems will have a better financial performance than those targeting gas-fired systems. Nevertheless, there are exceptions to this; an energy audit of the building is the best way to tell.
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