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Recommendations for Safe Operation of HVAC Systems Resulting from COVID-19

Issue 2: Thursday 14th 2020


It is recommended that PPMs are continued in a normal manner & possible increase to areas that may require more regular cleaning. No manufacturers can confirm that any cleaners for use on HVAC equipment will kill the COVID 19 virus, the disinfectants used by 360 are still the best viable option at present for use on HVAC systems. Drain traps to be regularly checked for water & topped up as required.

Continual Operation of Fresh Air Supply
The systems are to run 24 hours per day. Where this is not possible, they should be set to operate a minimum of of 2 Hours before the building goes into occupancy. The purpose is to provide as much ventilation as possible. It is suggested that all windows are opened even if there is mechanical ventilation.

Re-Circulation of Extract Air
It is highly recommended that there is NO recirculation of air from these units. Ensure that all the recirculation dampers are set to the “fully shut” position & the supply & extract dampers are in the “fully open” position. Where heat recovery ventilation is used, it must be verified that there is no exchange of air between the return air & supply air path. Where it is only energy that is exchanged & no air leakage between the supply & extract air paths, this can remain in place. Where there is contamination between supply & return air paths, this must be reprogrammed to bypass mode to prevent contamination between segregated areas.

Air Volumes, Supply & Extract
Air volumes should be increased from standard design conditions to allow for the maximum amount of fresh air supplied & stale air extracted. There may be additional noise resultant due to larger volumes of air passing through the existing duct work which is likely to have been designed for smaller volumes. Although subjective, any additional noise generated by the increases should not impact adversely on the working environment.

Heat Recovery, Thermal Wheels
Heat recovery via thermal wheel should be stopped. A heat recovery wheel mixes return air with fresh air & could be considered as a potential source of cross contamination. Reprogramming the controls to prevent heat recovery operation will stop the extract air mixing with the supply air & causing contamination.

Heat Recovery, Run-Around-Coils
A run-around-coil is usually a low temperature water circuit that will be used to pre-heat the fresh air in heating season. They do not have direct contact with the air & therefore, can be left to operate as normal as no cross contamination is possible.

Heat Recovery, VAM/Lossnay
The construction of the heat exchanger within these type of HRUs can allow some leakage between the supply & extract air paths. This allows for cross-contamination. They should be re-programmed into By-Pass Mode which allows full supply & extract without any heat recovery/recirculation.

Toilet Extract
Extract systems should be allowed to operate continuously. If they are controlled using PIR sensors, they should be re-programmed to allow for continuous operation. If there is no extract then a window should only be opened if it does not make the toilet a positive pressure compared to the rest of the building.

Natural Ventilation
The advice is to have as much ventilation as possible & that windows should be open. This also applies even if there is a ventilation system. The overall message is to create as much ventilation as possible.

Ventilation Purge Of The Building
Purging the building means to carry out a full extract operation to remove all air from the building & replace with total volume of ‘new’ fresh air. This should be carried out each evening, it should be programed to take place when the building is most likely to be unoccupied.

Increased Maintenance Regime
Maintaining cleanliness of systems is to be observed. Increasing maintenance visits to include anti-bacterial cleaning of coils & filters should be planned. Once it is established the conditions that will kill the virus, it may be possible to add relevant filtration to provide this.

Consequences of Removing Heat Recovery Operation
Ventilation without heat recovery will increase the load on the heating & cooling systems. The cooling & heating systems will have been designed with a tempered fresh air load. In removing the heat recovery function, the fresh air temperature will not be tempered & it may not be possible for the cooling & heating systems to maintain setpoint temperatures. It is only likely to occur during extremes of temperature, as the UK enjoys a relatively mild climate for most of the year, the systems have spare capacity outside of their maximum design conditions.

This will be a consequence of the increased load on the system from the untempered fresh air but it will be important to maintain both the supply & extract fresh air. Carbon Dioxide sensors should be added to ensure ventilation is proportionate to occupation & consideration to setting frequent air purges in areas of high occupation.

Consequences of Increasing Fresh Air Volumes
Energy consumption will increase as heating & cooling systems work to maintain setpoint against an increased fresh air volume & an increased fresh air volumes without being pre-tempered.

Air Conditioning Systems

Risk Assessing Operation of AC Systems
Risk assessing operation of AC on an individual basis should be carried out. There are a variety of opinions regarding safety & benefits of AC in relation to spread of Covid-19. The various governing bodies that collate & disseminate guidance have not reached a single conclusion. Until a clear directive is settled upon, we give here the various considerations to be made before making the decision on whether to operate or disable AC systems within your buildings. As mentioned, the decisions must be made on a case by case basis.

Fan Coil Units, Water & DX
Where FCUs are located without a void & are also being used to supply the fresh air into the room, then they must continue to be in operation. The benefits of fresh air supply to the space will take precedent.

Operation of FCUs
The safe operation of FCUs will be based upon the areas served & if operating it could enable cross-contamination to other areas i.e. where an FCU serves two different spaces. All FCUs use recirculated air which is known as ‘Return Air’. It is either positively connected to the FCU via ductwork or is left open to draw air from its immediate location, this is called Free Back Return. Cross-contamination comes from the Return Air function. An FCU supplying 2 different areas is at risk because of the return air. If the return air comes entirely from Space #1, then Space #2 will be contaminated by air from Space #1. If return air comes from both spaces, both spaces will be contaminated by each other’s air. If the return air comes from a neutral 3rd space, both spaces are again contaminated by the air from the neutral 3rd space. Some FCUs may have a proportion of the return air made up of fresh air, however as it is not possible to introduce 100% fresh air to a FCU, it is not possible to prevent cross-contamination where an FCU serves more than 1 area.

FCU Serving More than 1 Area
Where a single FCU is being used to serve 2 or more spaces, cross contamination of the air will occur either via the return air path as described above. The return air is facilitating cross-contamination which should be removed. To overcome this, consider the fresh air/ventilation considerations & take one of the following actions most appropriate to the building:

  1. 1. Reprogram the controls to isolate that FCU so it cannot operate at all. Only practical if there is an independent fresh air supply to both spaces; mechanical or opening windows.
  2. Modify the ductwork so that the fan coil can supply to & return from a single space. It will mean that the 2nd space has no AC but as long as there is an independent fresh air supply (mechanical or opening windows) the room will still be usable.
  3. If modifications cannot occur then the rooms should be deemed out of use with appropriate signage.

Installation of New FCUs
On any new installations In order to minimise person to person contact inadvertently, return air & supply air grilles must be located in the same area & serve that area only. It must no longer be an option to allow a single fan coil to serve more than one office. Maintaining this standard will ensure those working within an office are inhaling recycled air from this demise & population only & not subjected to recycled air from additional population.

Illustration Showing Potential for Cross-Contamination of Fan Coil Serving More Than 1 Area

Wired & Infra-Red Controllers
Wall mounted & infra-red hand held controllers are used to control FCUs. They provide a high risk source of potential for contamination as the virus can be spread via touch & can remain active on surfaces for up to 7 days. Where possible they should be removed & all control should be via a centralised controller which can be accessed by a single individual.

If controllers are removed, they should be carefully catalogued & stored securely as it may not be possible to purchase replacements if they go missing or are unaccounted. If we assume that at some point we will return to normal controllers can be reinstated, those old controllers will be put back into service.

If it is not possible to remove controllers they should be cleaned regularly & control changes should be discouraged but only take place after cleaning. Sanitiser should be at hand so that users of the controls sanitise their hands before & after use as a failsafe precaution.

Centralised Controls
Centralised controllers should be programmed with timeclocks & set points to establish any revised operation of the HVAC. Any equipment that should not operate during this time should be disabled at the centralised to prevent any override. Central controllers should be accessible by as few people as possible. They should be cleaned before & after any use & sanitiser should be close at hand for users to use before & after.

Increased Maintenance Regime
Maintaining cleanliness of systems is to be observed. Increasing maintenance visits to include anti-bacterial cleaning of coils & filters should be planned. Once it is established the conditions that will kill the virus, it may be possible to add relevant filtration to provide this.

Using the AC to Prevent Virus Spread
Once it is known at what temperatures the virus Is killed, it may be possible to use the AC coils to kill the virus. For example, if the virus cannot survive on surfaces above 40°C or below 4°C it may be possible to utilise some test or commissioning modes on the AC system to generate those temperatures on the coil & run the system for a sufficient period of time to ‘disinfect’ the air of an area via the temperature of the AC coil. This cannot be a consideration until the temperatures at which the virus cannot survive are known & the AC manufacturers can confirm that those temperatures can be maintained on the coil for sufficient period of time.

Ductwork & Grilles
All supply & extract grilles should be opened to ensure all areas served have air circulation. Systems should be rebalanced & new air volumes recorded.

Future Developments
We are investigating the effectiveness of UVC light & how it may be used within an HVAC system to prevent the spread of Covid-19. It is a relatively unknown way to kill viruses outside of the medical environment & requires further & detailed research. However we are following the development of this & its potential within our industry.

As progress is made on the deployment of this technology, we will update our knowledge & skills as necessary in order to advise & offer any solutions appropriate.

Once more is known about the virus, more can be done.

Guidance Notes
The information contained has been obtained using BESA (Building Engineering Services Association) guidance with information from REVHA (Hygiene Requirements for Ventilation & Air Conditioning) & references to CIBSE (Chartered Institution of Building Services Engineers). It is based on their current documentation & recommendations.

  • This list is not exhaustive & a risk assessment of all areas is advised before people return to their workspace.
  • This information is constantly changing & is intended for guidance only.
  • 360 cannot be held responsible for any situations that occur as a result of this information.
  • The advice is based upon minimising COVID-19 spread from air conditioning systems & is not relevant to any environment or energy policies.
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