Electric heating systems have the advantage of not requiring fossil fuel combustion inside a building, which contributes to lower emissions in urban areas. However, one cannot assume that a heating system is 100% free of emissions just because it uses electricity - to determine its real environmental impact, the power sources used by the local utility company must be considered.
However, even if the local grid depends on fossil fuels, electric heating is a good starting point towards decarbonization. If many buildings use heating systems that run with electricity, a greener power grid leads directly to reduced heating emissions. On the other hand, the opportunities to use renewable biofuels for combustion heating are limited, and biofuels still produce emissions.
Design a clean heating system for your next building project.
What Is Electric Heating?
The concept of electric heating can be used to describe two very different types of space heating systems: resistance heaters and heat pumps.
Electric resistance heating is a simple concept: Voltage is applied to a heating element, and the resulting current causes heat release. Unfortunately, you can only get one kilowatt-hour of heat for every kilowatt hour of electricity, and this leads to a very high operating cost.
Heat pumps are more complex devices than resistance heaters, and they can be described as air conditioners operating in reverse. While an air conditioner removes heat from indoor air, a heat pump extracts thermal energy from outdoor air to release it inside.
The operation of a heat pump may appear counterintuitive, since the device is extracting heat from cold outdoor air. However, consider that all substances have thermal energy unless they are at absolute zero (-273.15°C or 0 K). In other words, outdoor air feels cold to humans during winter, but it still contains a lot of energy. A heat pump uses the compression, condensation and evaporation of a refrigerant to capture this heat for indoor use.
For a given heating capacity, heat pumps normally have a higher upfront cost than resistance heaters. However, their electricity savings typically exceed 40%, and the most efficient models can yield savings above 80%. As a quick example, assume you will compare both options based on an electricity tariff of 20 cents/kWh.
A 5-kW resistance heater needs an electricity input of 5 kW as well. The consumption for 10 hours of operation is 50 kWh, which results in $10.
A 5-kW heat pump with a Coefficient of Performance (COP) of 2.5 only uses 2 kW (60% savings). The consumption for 10 hours of use is reduced to 20 kWh, with a cost of $4.
A more efficient heat pump with a COP of 5 would only use 1 kW, spending only $2 in 10 hours of operation.
With modern electricity rates, resistance heaters have a prohibitive operating cost for most building owners. When developers want to avoid local fuel combustion and emissions, HVAC engineers normally recommend a heat pump system.
How Renewable Power Benefits Electric Heating
A common argument against electric heating as an green option is that emissions are produced somewhere else, since fossil fuels are still the dominant energy source for power plants. However, electric heating brings two advantages even in this case:
Emissions are moved away from buildings, reducing the urban concentration of harmful combustion products.
When dealing with emissions, power plants are subject to much more stringent controls than buildings. While emissions are produced in both cases, power plants often have additional measures to mitigate them.
Consider that many states have deployed laws called Renewable Portfolio Standards (RPS), which drive a constant transition to clean power. An RPS law establishes a minimum renewable energy percentage for investor-owned utilities, and it also sets a deadline. There are severe penalties for utilities that fail to meet the RPS requirements.
With electric heating systems, owners can switch from the power grid to an on-site electricity source with less emissions. Also, when utility companies increase their share of renewable power, electric heating systems become greener automatically.
Brief Recommendations for Electric Heating
Like in any engineering project, you can achieve optimal results with electric heating if the systems is properly sized according to building needs. Purchasing a heating system based on rules of thumb is not recommended, since undersized and oversized installations both have performance issues. The best recommendation is getting a heating design from a professional MEP engineering firm.
The local weather must also be considered, since air-source heat pumps have a minimum outdoor temperature at which they can operate. The top heat pump manufacturers normally design their products for temperatures as low as -4°F, but some units for the extreme cold can operate at temperatures below -10°F or even -20°F.