Building interiors would not be suitable for long-term occupancy without heating, ventilation and air conditioning. Space heating systems keep a comfortable indoor temperature during winter, and air conditioning systems accomplish the same function during summer. Ventilation systems constantly replenish indoor air, preventing the accumulation of pollutants, and they circulate air through heating and cooling equipment to keep optimal temperatures in the entire building.
However, the benefits of HVAC equipment come with considerable costs. Space heating and air conditioning systems normally have a much higher energy consumption than other equipment in residential and commercial buildings. In addition, the upfront cost of HVAC installations is significant.
Ideally, HVAC systems should keep comfortable indoor temperatures and preserve air quality, while having the lowest energy consumption possible. HVAC equipment should also operate with minimal noise and vibration - both effects cause discomfort, and vibration can also cause premature equipment failures.
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HVAC performance tends to degrade over time, leading to poor temperature control, inefficiency, reduced air quality, and increased noise and vibration. As part of your building maintenance plan, all four aspects should be monitored regularly.
1) Improving Temperature Control
Heating and cooling systems should keep a comfortable temperature all year long. Oversizing equipment is a common but incorrect engineering practice, which leads to excessive cooling during summer and excessive heating during winter. In addition to wasting energy, overheating and overcooling can lead to health issues, since occupants are exposed to a drastic difference between indoor and outdoor temperature.
The simplest way to deliver the right temperature is having HVAC systems that are properly sized and configured. Modern heating and cooling equipment allows greater control, but options are limited for older systems. The best approach depends on the specific conditions of each project: it may be possible to optimise the existing equipment, but upgrades are cost-effective in many cases, especially when the existing installations are older and lacking in maintenance.
2) Improving Energy Efficiency
Since heating and cooling systems have a higher energy consumption than other building equipment, efficiency improvements offer a drastic reduction in their operating costs. Temperature control and energy efficiency are closely related - both are achieved simultaneously when HVAC equipment is properly sized and configured.
HVAC efficiency can be enhanced further with speed control for compressors, pumps, fans and other motor-driven components. When the full capacity of this equipment is not required, reduced speed operation is much more efficient than intermittent operation. Speed control can also extend the service life of equipment, since frequent starts and stops are mechanically demanding and cause accelerated wear.
3) Improving Indoor Air Quality
Indoor air quality tends to receive less attention than energy efficiency, but it is fundamental for a healthy indoor environment. To achieve air quality, you must keep humidity at an optimal level, while preventing the accumulation of air pollutants.
ASHRAE recommends a relative humidity in the range of 30% to 60%, since many issues arise when it falls outside of this range.
- Excessive humidity causes the proliferation of mold, dust mites, bacteria and viruses. Mold and dust mites cause allergies, while bacteria and viruses are the direct cause of many diseases. If humidity is combined with excessive air conditioning, you can end up with a very uncomfortable environment that feels like a refrigerator.
- On the other hand, excessive dryness can cause eye and skin irritation. Dust, viruses and other particles also remain airborne for a longer time when humidity is low.
With air pollutant concentrations, the approach is different - their levels must simply be kept as low as possible, not within an optimal range. However, it is important to note that not all pollutants are equal:
- Contrary to popular belief, carbon dioxide (CO2) only becomes dangerous for humans at very high concentrations that are unlikely in homes and businesses. Although the effect of carbon dioxide on global climate is severe, it does not generally pose a hazard for humans. Concentration must rise to about 10% for carbon dioxide to be lethal, but you need extremely poor ventilation to reach even 1%.
- Carbon monoxide (CO) is much more dangerous, since a concentration of just 1% causes death within minutes. Since carbon monoxide is a combustion product, building codes mandate its use in the USA.
- Volatile organic compounds (VOC) are substances that evaporate at room temperature and atmospheric pressure, and they have been associated with allergies and health conditions like asthma. VOCs are found in paint, new furniture and many cleaning products, and many actually have a pleasant smell… making them more dangerous. They are not lethal like carbon monoxide, but exposure to them is detrimental for health.
- Particulate matter (PM) is composed of suspended particles, where some are formed from VOCs and others are combustion products. PM has also been linked with health conditions such as lung and heart disease.
It would be possible to write an encyclopedia about air pollutants - this is just a brief list describing some relevant examples for building interiors. A well-designed ventilation system helps control all of them, with a constant supply of outdoor air. There is a common misconception that outdoor air is more polluted, but the US Environmental Protection Agency has found that pollutant concentrations are 2 to 5 times higher indoors.
4) Reducing Noise and Vibration
Although noise and vibration are separate issues, they are almost always found together in HVAC equipment. Although some degree of noise and vibration is inevitable with large equipment, their effect is minimized with adequate supports such as springs or damping pads. When designing the layout of a building, the recommendation is to place mechanical rooms far from areas that are susceptible to noise and vibration.
Excessive noise and vibration are a clear warning sign that your equipment needs maintenance. Noise can cause discomfort and difficulty concentrating, while vibration can damage equipment. When vibration propagates to components other than the source, additional noise is produced.
If your energy expenses have been increasing and your building interior has become noisier, it is time to get a professional inspection of your mechanical equipment. In addition, temperature and humidity extremes indicate your HVAC systems may be of the wrong capacity or configured incorrectly.
If HVAC performance has diminished, also check if there has been an effect on occupant health. For example, if sick leave has become more common in an office building, there could be humidity and mold issues.