Electricity and gas bills represent a large portion of operating costs for property owners. However, energy efficiency is a technically complex topic, and the most effective measures to reduce utility bills are not always evident. The best recommendation is getting in touch with engineering consultants for a professional energy audit, but being informed about the topic is also of great help.
The US Department of Energy has many useful sources for building owners, such as the Energy Saver website. The US DOE web resource includes detailed descriptions of all systems that consume energy in buildings, along with recommendations to achieve top performance. This article provides a brief overview of the main topics covered in their Energy Saver website.
Energy efficiency does not depend on a single building system. You also have to consider how different installations interact with each other, the effect of the building envelope, and the energy consumption habits of occupants. For example, you can have air conditioning systems of the same capacity for buildings of the same floor area, but you will find that power bills differ drastically depending on specific building conditions and usage habits.
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Heating and Cooling Systems
Since heating and cooling represent the largest energy expenses in most residential and commercial buildings, many publications from the US Department of Energy focus on this area. Buildings can achieve optimal HVAC performance when their heating and cooling systems meet the following conditions:
- Having the right capacity according to the load and climate zone.
- Equipment with a high energy efficiency rating.
- Thermostats and controls are configured correctly.
Thermostats have a fundamental role in heating and cooling systems, since they determine how equipment operates. A poorly configured thermostat can cause inefficient operation and energy waste, even if you have the most efficient heating and cooling equipment in the market. The opposite also applies: a thermostat that is configured properly can save energy even when the efficiency of heating and cooling equipment is moderate.
In general, the temperature set point of a thermostat must be as high as possible during summer and as low as possible during winter, while staying within a temperature range that is healthy and comfortable for occupants. Unfortunately, a common practice is setting the thermostat as low as possible during summer and as high as possible during winter, and this has two negative consequences:
- Since the temperature difference between outdoor and indoor air is so high, air conditioners and space heaters have to work longer periods.
- The higher temperature difference also increases summer heat gain and winter heat loss. Remember that heat transfer is faster when a temperature difference is higher.
In other words, extreme thermostat settings not only increase the heating and cooling load on your HVAC equipment. They also make your building less efficient because unwanted heat gain and heat loss are accelerated. The US DOE strongly recommends programmable thermostats, which learn occupant habits and adjust the temperature set point automatically; having to adjust a manual thermostat continuously can be tedious and easy to forget.
Air ducts are another element of HVAC systems that is often ignored, since they are normally hidden from sight. When duct systems suffer from air leaks or poor insulation, they can cause a massive energy waste throughout the year, driving up both electricity and gas bills.
Ideally, ducts should have adequate insulation and air-tightness, while being free of obstructions that disrupt airflow. When possible, the US DOE recommends installing ducts inside conditioned spaces, since this minimizes the energy losses caused by air leaks. Even with a well-designed duct system, air leaks are very difficult to eliminate completely.
Heating and cooling equipment is characterized by variety, and the best option for each case is determined by building conditions. Cooling equipment normally runs with electricity, although some industrial applications favor the use of absorption chillers, which can run with waste heat from manufacturing processes or power generation. Heating equipment is available for a wider variety of energy inputs, including electricity and fossil fuels like natural gas, heating oil or propane.
Combustion heaters are often preferred over resistance heaters because they have much lower running costs. However, heat pumps are a modern alternative that can match the cost of combustion heaters without the emissions. Based on how they exchange heat with building exteriors, heat pumps are classified as air-source, water-source or ground-source units.
Importance of Building Design and Weatherization
The US DOE also emphasizes the importance of building design and weatherization when dealing with energy performance. Having HVAC systems that are smart and efficient is great for energy savings, but you must also ensure that the building itself is designed for high performance. Buildings should be designed to minimize unwanted heat gain (summer) and heat loss (winter), and both insulation and air-tightness are important to achieve this.
Building envelope upgrades range from very simple and affordable options like caulking and weatherstripping, to more complex projects such as replacing your fenestration with triple-pane windows. Air leaks and poorly-insulated spots can sometimes be hard to find; they are often hidden in basements or the intersections between walls and roof structures.
Conventional HVAC design focuses on temperature control, but indoor air humidity is also an important factor. Heating and cooling systems operate less efficiently when buildings have poor humidity control, and some construction materials are vulnerable to damage from accumulated moisture. In addition, air humidity stimulates the growth of mold, which has a detrimental effect on indoor air quality - mold spores cause irritation and allergies, and can potentially worsen the symptoms of asthma patients.
Lighting Efficiency and Sunlight
The Energy Saver website suggests a reduction of your lighting costs by following two complementary strategies:
- Using lighting products with the highest efficiency ratings, ideally LED lamps and fixtures with ENERGY STAR labels.
- Optimizing your window layout to maximize solar lighting. However, indirect lighting is preferred, in order to prevent glare and unwanted solar heating. There are energy-efficient skylights that draw sunlight into a building while blocking the heating effect.
Daylight-responsive controls that can adjust the output of lighting systems based on the natural lighting level achieved with windows and skylights. These systems can help building owners achieve the highest possible lighting efficiency.
In addition to providing free lighting, sunlight can also be used as an energy source if the building is equipped with a photovoltaic array. Solar power is one of the most cost-effective building upgrades, considering that the technology becomes more affordable each year, while electricity tariffs tend to increase.
The Energy Saver website provides useful recommendations for buildings of all types and their internal MEP systems. However, additional attention is given to the topics discussed in this article, since they have the highest energy-saving potential. A high-performance building envelope combined with efficient HVAC and lighting is guaranteed to achieve low energy costs, especially if the building also has enough space for a solar power system.