Buildings are responsible for around 40 percent of the global energy consumption, making it imperative to decrease consumption and increase energy efficiency in buildings. At the same time, we spend almost 90 percent of our time indoors. The trick is to reduce energy consumption without compromising indoor climate.Correct room temperature and ventilation is paramount to health, comfort and productivity. On the other hand, energy prices are soaring and there is a general global need to lower energy consumption. A good way to reach both these targets is to ensure that air handling units (AHU) are operating correctly. It is good practice to go through the HVAC systems when switching tenants, and adjust them to the needs for the new tenant, but it may in these times be worth to go through the systems no matter the occasion.
There are five crucial factors
There are five crucial factors to consider when aiming for a lowered energy consumption, namely: airflow, operating time, demand control, temperature and maintenance. All which should be handled with care to ensure a comfortable indoor climate for the people inside.
Adjusting the airflow to the actual facility needs is important. Too low an airflow might cause discomfort, lowered productivity and health issues, while too high an airflow might result in draughts and sound which are disturbing to the people inside the building. Further, a too high airflow causes higher energy consumption. Reducing the airflow by 10 percent can result in 20 percent lower energy consumption in fans.
Reducing the AHU operating time will give a corresponding reduction in the unit’s power consumption, so make sure that the daily and weekly schedules are correct for the type of activity and occupancy in the facility. Also, the AHU might be able to run at a reduced rate or even be turned off completely during holiday seasons, vacation periods and bank holidays when no one is expected to be in the building. Be aware, if the system is shut off completely for a period of time, it is vital to make sure that it is clean and dry to avoid mold and other organic growth. If possible, it is a better option to simply reduce the airflow during downtimes.
The power consumption of a fan increases rapidly with increasing airflow. Using a demand control system can make for significant energy savings and increased comfort for the people inside. Variable air volume (VAV) is considerably more power-saving than constant air volume (CAV), but the minuscule automatic adjustments in a properly tuned demand controlled ventilation (DCV) system can save even more. If a CAV system is in place, consider a strategy of only making selected parts of the building available for use and thereby allowing ventilation to be reduced in the empty areas. As a CAV system is usually set for a maximum number of people inside, a sparsely occupied space can be found uncomfortable from an indoor climate perspective.
Setting the supply air temperature a few degrees lower can save heat energy without a notable impact on comfort or productivity, unless the new temperature is far from the recommended 21 degrees Celsius. Further, air distribution efficiency actually increases with a supply air temperature a few degrees lower than room temperature which is favourable. Lowering the temperature setpoint by a couple of degrees reduces the energy required for heating. If the system is provided with energy recovery, the need for additional heating and/or cooling is also significantly reduced. However, bear in mind that a too low (or too high, for that matter) room temperature has a negative impact on productivity. And bear in mind, that reducing the setpoint temperature works best in newer, better insulated buildings – in older buildings, temperatures near walls and windows might get too low with a reduced indoor temperature and hence uncomfortable.
Regularly scheduled maintenance is important to keep energy efficiency up – poorly installed, commissioned and serviced systems consume significantly more energy. For example, changing filters in time is perhaps one of the easiest ways to save energy, since AHUs with clogged filters run their fans harder to compensate for an increased pressure drop. Other potential problem areas include: poorly balanced ventilation systems, poorly commissioned hydronic systems, and air in hydronic systems, the latter can come from the use of plastic pipes that let in small amounts of air. All the above will lower the efficiency significantly. An important part of regular maintenance is to measure, visualise, analyse and react, repeat as needed. Even older systems can benefit from adding modern sensors, which is not necessarily a huge cost these days and is likely to be preferred over excessive energy consumption and the risk of delivering a poor indoor climate.
A final measure
A critical energy-failure is when heating and cooling is carried out by different solutions, aiming for different set points. Having radiators heating and ventilation cooling – in the same space, at the same time - is obviously counterproductive and costly. By making sure the temperature set points are aligned between the solutions both energy-efficiency and indoor comfort can be ensured, people can feel good inside.
So, there are a number of factors and measures to consider when looking for ways to reduce the energy consumption of an HVAC-solution. It is though essential to keep the people in the building in mind, energy savings should not compromise the indoor climate.
Further reading on the topic of energy-savings are found in our blog section, here.