It has long been known that cleaning the cooling coils of air treatment plants saves energy (see the ASHRAE Journal, Nov. 2006, "Study Verifies Coil Cleaning Saves Energy").
In 2016, NADCA addressed the issue through publication of the White Paper "Restoring Energy Efficiency Through HVAC Air Distribution System Cleaning", which provided guidelines on how to assess the significant improvement in terms of energy performance after the restoration of an HVAC system.
The survey results showed that improvements in cooling capacity and airflow are a typical result of plant remediation. The latter should therefore be considered as an integral part of any program aimed at improving the efficiency and energy saving of a building.
A task force of NADCA members was sent to detect these parameters in the field before and after the remediation work to determine the effect that cleaning has on energy performance. The test took place in different regions of the United States and Canada, testing many types of HVAC systems, installed in commercial and residential settings.
The tests were carried out before and after the cleaning of the plants, following a process that included the measurement, before and after the evaporator battery (cooling), of the temperature and the air flow (quantity of air moving inside the system).
Almost all of the cases studied showed that the cleaning of the plants brought significant improvements in the energy efficiency of the plants themselves.
As regards the Temperature Difference (ΔT) measured before and after the heat exchange battery, in residential systems the tests showed that the cleaning operations showed an average improvement of 5.9 ° C, equal to 61% (one passed from a T of 9.6 ° C before cleaning, at 15.5 ° C after cleaning). In the commercial sphere, the improvement was limited but still significant, settling at 5.4 ° C, equal to 40% (it went from a T of 13.6 ° C before cleaning, to one of 19.0 ° C after cleaning).
As far as the Airflow is concerned, the study showed that cleaning the system, removing obstructions from the battery, from the ducts, from the deflectors, from the vents etc., increases the air flow that moves through the system. In particular, in residential systems, an 11% average increase in the quantity of air transported was detected, while in those installed in the commercial sector the average increase was much higher, reaching upwards of 54%.
The cooling capacity (or heat transfer rate, expressed in BTU) of the plants subjected to the survey, after cleaning resulted in an average increase of 150% in the residential area and 225% in the commercial sphere.
Waste from list in the pipeline network
A further element of energy (and therefore economic) waste is constituted by the leaks and cracks that often present the duct work.
The US Department of Energy highlights that a leaky network of aeraulic pipelines is one of the greatest contributions to energy waste in buildings and classifies duct sealing as one of the most effective remedies for reducing overall energy costs.
First of all, a plant with fractured ducts, which show pressure drops, needs a greater amount of energy to circulate the air through the building. If we consider that the one necessary to operate the fans represents 20-60% of the total energy consumption used by the air treatment plants, we understand how a simple 15% reduction in losses can reduce the fan's energy needs by 40% and save thousands of euros every month.
Secondly, the leaks in the aeraulic pipelines disperse the air conditioning along their path and therefore make it necessary to introduce a greater quantity of external air into the building, in order to be able to convey it in all the rooms in the right quantities. Keeping in mind, this extra air coming from outside must be heated, or cooled, and this causes a significant increase in the energy cost necessary for the operation of the plant.
The waste resulting from "useless cleaning"
A significant fact that few companies realize: for a significant part of HVAC plants in poor hygienic conditions, cleaning alone is useless.
We need to know how to investigate why contamination has occurred. Sometimes contamination is not solely a physiological phenomenon, because it derives from plant or structural deficits. Damaged or inadequate filtering sections, poorly positioned outside air intakes, non-functioning drainage lines, leaks in the ducts, proximity to evaporative towers, unbalance phenomena, are just some of the possible causes of dangerous contamination.
In these cases, cleaning the system without solving the problem upstream is like throwing money away. However, to understand what the underlying problem may be, skills and experience are needed. It is necessary to carry out an adequate Aeraulic Risk Assessment, which includes a thorough hygienic-plant analysis.
And too many companies on the market today do not have the training and specialization necessary to make an accurate diagnosis of the causes and mechanisms of propagation of contamination in air treatment plants.
They offer only a cleaning service and this, as well as being useless, can also be dangerous.