Covid Management Issues
Covid solutions is an multi-step process starting with proper equipment assessment and continuing to long-term data tracking and automatic performance analysis.
Start with the obvious: outside air introduction into the occupied space. Outside air ventilation provides the first opportunity to ensure that indoor space air quality meets minimum IAQ recommendations, all while providing fresh air for occupants during occupied hours.
Verify the correct outside air ventilation rates first. Measure OA CFM. Check damper actuators. Verify operation minimally corresponds to fan operation
Outside Air Ventilation
HVAC units are designed to admit ventilation outside air during normal runtimes. Actuator driven outside air dampers open and close to admit code-prescribed air as a percentage of unit CFM capacity.
Outside Air BenefitsAir quantities can be optimized using indoor air sensors like CO2. But today's indoor air quality goes beyond code settings and looks for outside air introduction that is also optimized by occupant count, volatile organic compounds, relative humidity, lighting levels, barometric pressure, and even noise.
Maintenance Equipment operation is not a given. Routine maintenance may or may not ensure best-levels of outside ventilation air. Dampers sometimes remain fixed with the fan on or off. Outside air intake filters become clogged or go missing entirely.
Optimized Outside AirHVAC unit outside air quantities are adjustable. Opening to an assumed correct fixed position is not necessary using space sensor feedback. Optimized outside air quantities reduce energy cost while supporting better indoor air quality. Today the process can be better - much better.
Free economizer cooling is available during outside air temperatures from 50/55F to 70/75F. Outside air is drawn into the HVAC system - up to 100% - to provide cooling supply air. Economizers work but need attention and maintenance. Verify changeover temperatures from outside air to mechanical cooling. Confirm damper minimum position is sufficient or necessary. Use additional indoor space sensing to auto-adjust outside air introduction.
Outside Air Economizer
Environmental BenefitsEconomizers have an additional benefit in today's virus-type environment: they flush occupant spaces with up to 100% fresh air to help remove airborne particle nuclei.
Advance ControlsEconomizer operating controls manage supply air temperatures using a combination of outside air and refrigeration compressors. Long-term issues are primarily caused by mechanical problems with return and outside air dampers. Rooftop units equipped with powered exhaust improve system performance by helping remove space return air.
Side ConditionsOutside air quantities operate up to 100% and, if outside air has a high RH%, cause additional pressure drop across the filters. Good maintenance is important.
Reliable OperationTracking economizer operation becomes even more important over time. Alerts are important to flag unexpected operation. Still, there is no better way to flush occupied space than with an economizer.
Effective space air delivery ensures positive nuclei particle pickup and capture in filters or HVAC exhaust. Casual return air ductwork and grill sizing diminish air circulation effectiveness.
Effective air circulation takes on additional importance in keeping space conditions clean. It also minimizes space temperature differences to improve comfort.
Room Air Distribution
Room Air CirculationSupply air movement in a space induces room air circulation that impacts particle pickup. The ability to induce air movement depends on the type of supply air diffuser. Variable air volume (VAV) systems reduce air supply quantity and corresponding air inducement.
Return Air EffectivenessSimple eggcrate grills into plenum ceilings may reduce overall air quantities. Grill location and size takes on greater importance. Economizer performance often suffers from insufficient or improperly located return air grills.
Dust PickupSpace air movement determines dust pickup ability and the corresponding ability to keep the space cleaner.
Virus CaptureVirus nuclei float in the air especially during dry winter relative humidity conditions. To the extent these nuclei attach to dust particles they can be conveyed to the HVAC system for capture in a high efficiency filter.
Most HVAC systems view filtration as a way to keep the cooling coil clean.
But filtration can do more than simple coil protection. Low effectiveness filtration can be replaced with much higher small particle capture at a small additional pressure drop.
HVAC Air FiltrationKeeping CleanBetter filtration improves virus pickup, capture, and deactivation. Filters have gradually transitioned from flat media to folder large-surface media. Today's folded media is now available up to MERV 13.
Improved Dust CaptureParticles that used to slip through media now are readily captured. Use high-quality filtration in every case.
Pressure Drop TradeoffImproved media performance comes at the expense of additional pressure drop. CFM drops off, often unacceptably, as filter performance goes up. Performance tradeoff can be minimized using ionization to increase particle size. A MERV 8 filter permits more CFM at reduced pressure yet still captures dust particles holding droplet nuclei.
Negative Air Ions
Negative Air Ions (NAI) impact both human health and indoor air quality. They help relieve symptoms of allergies to dust, mold spores, and other allergens.
NAI is also an effective method for removing particulate matter (PMs). They are especially effective with PMs diameters of less than 10 microns (PM10).
NAIs have been shown to impact individual performance in drawing, visual reaction time, and auditory response.
NAIs are also known to be effective in relieving symptoms of seasonal affective disorder (SAD). They also have shown to be effective at treatment of chronic depression.
Reports show that NAIs attach themselves to dust, spores, and other allergens, which helps to relieve symptoms of allergies to these particles.
Negative Air Ionization
Proven EffectivenessNegative air ionization is a known method for cleaning air. It's often associated with a clean smell after thunderstorms. Today's ionization devices have evolved into both cleaning air as well as improving psychological health, productivity, and overall well-being.
Negative Air Ion GenerationAir ions are electrically charged molecules or atoms in the atmosphere. Air ions are formed when they gain an ion. Sources including radiant rays in the atmosphere, sunlight including ultraviolet, corona discharge including thunder and lightning, shear forces of water (Lenard effect), and plant-based sources of energy.
Building ApplicationsIon generation for building HVAC is provided by an array of devices usually mounted in ductwork near air distribution diffusers. UV light is one source of NAIs but the primary source is from suitably mounted ion generating devices.
Ion GeneratorsGenerators use a high voltage to create a corona discharge. Voltage levels are regulated to avoid the creation of ozone. Generators rely on a chain reaction process called an electron avalanche. NAIs are not stable and will gradually decay - as low as 100 seconds. A continuous discharge, therefore, is required. The ability to deliver ions to a space impacts their effectiveness. Supply air ductwork and ion generator location within is important.
Ion ClustersNAIs are composed of multiple negatively charged molecules. Negative ions combine with multiple water molecules to form negative-ion clusters. These clusters attract viruses and other particles using a process described as aggomulation. Larger ion clusters more readily make their way to HVAC filtration systems for capture.
Ion ConcentrationNegative ion concentration exceeding 1000 ions/cm3 is widely regarded as the threshed value for fresh air. Ion generators are designed to increase to levels from 3,000 to 10,000 ions/cm3. The level of ion delivery is directly a function of generator placement and location in respect to supply air diffusers.
Ultraviolet light is widely used in hospitals, restaurants, and grocery stores to minimize airborne viruses as well as mold and bacteria.
Ultraviolet light is also used to irradiate surfaces through the use of light wands where individual objects are targeted for cleanup.
UV-C is straightforward to install and effective in operation - continuously.
Proven EffectivenessUltraviolet light has long been used to kill viruses. It is a proven method, for over 100 years, to deactivate viruses. But it's direct use in the space is limited because of potential eye impact. Ultraviolet C restricts frequencies to +/- 264 microns, known to be most effective with viruses.
Killing AbilityUltraviolet germicidal irradiation (UVGI) can be deployed in HVAC equipment to kill viruses on filter media. Depending on media installation it can also effectively keep cooling coils from building up mold and bacteria during the cooling season.
Practical SolutionInstalling UV-C lights in HVAC units and ductwork is simple and practical. It avoids direct visual impact by space occupants. And it offers the additional benefit of keeping units clean on a continuing basis.
Equipment Performance Tracking
Confidence that HVAC equipment is performing as expected requires key temperature tracking.
Only extended data tracking can create the type of information to automatically assess system operating alerts.
Tracking EffectivenessDelivered air needs to be tracked for performance. Outside air in combination with return air produce mixed air for direct or cooled supply to the space. The questions to resolve are: does the equipment function effectively; is outside air being admitted as expected; is refrigeration removing sufficient moisture from the air; is the pressure drop across the filter reducing air flow.
Data LoggingExtended data logging provides weeks to years of comparative for data for long-term analysis. Data is collected to a cloud high-speed database for security. Data is collected fast enough to catch compressor short-cycling along with unexpected extended runtimes. Automated backups provide confidence that extended system analysis will continue.
Temperature DataEffective tracking involves multiple temperature sensors attached to key operating points in the system. Temperatures are used in lieu of pressure data where appropriate.
Alerts provide notifications of equipment operating outside normal limits. This analysis continues 24x7 looking for conditions indicating equipment not performing properly.
Alerts report on complete equipment failures but focus on subtle operating conditions that fail to meet performance criteria by small margins.
Tracking gathers the data and alerts analyze it for out-of-normal operation. Alerts are extensive including:
- Discharge air too high or too low for given outside air temperatures and expected cooling or heating.
- Mixed air operating excessively cool or warm given heating and cooling demands in the space for the needed heating and cooling.
- Mixed air operating alerts check for economizer temperatures with respect to outside air conditions.
- Mixed air damper operation is tracked for admitting outside air suitable for cooling space conditions and first stage of refrigeration.
- Space return air temperatures are monitored for appropriate limits in context of current heating and cooling needs.
- Refrigeration suction pressure is checked for low refrigerant gas condition reflected in supply air discharge air temperatures.
- Head pressure temperatures are verified as appropriate for outside air temperatures.
- Refrigeration coil suction and liquid temperatures are verified as appropriate for a given head pressure, outside air temperature and call for cooling.