Many industries use pressurised rooms to stop cross-contamination between one area of a building and another. For example, semiconductor makers use positive pressure rooms (PPR) to ensure their integrated chips are free of contaminants in the air. Hospitals and clinics employ negative pressure rooms (NPR) to contain the spread of infectious diseases. The difference between positive vs negative pressure rooms is mostly one of pressure differential and air flow. Both approaches use air pressure differentials to control ventilation and contamination.
Pressure Differential
Anyone who’s ever let go of an un-knotted balloon has witnessed the propensity of air to move from a higher pressure area to a lower one. The bigger the pressure differential, the faster the balloon will fly around the room. Building managers use HVAC equipment, fans and ventilation systems to control this natural propensity of air to escape—to keep the “balloon” knotted as it were.
The natural movement of air without the aid of mechanical equipment like a fan is called “passive” air flow, and techs use passive air flow to keep debris and contaminants from entering or exiting a room. If done correctly, the result is a stable environment with lower or higher air pressure than the surrounding area.
What’s a Negative Pressure Room?
To create a NPR, HVAC professionals must move air out at a faster rate than it comes in. That is, a negative quantity of air maintained. The purpose is to control the direction of passive airflow. When someone opens the door of an NPR, negative pressure draws passive air inside, forming a barrier against the escape of pathogens or dust. Interior air then moves through a filtration system to remove contaminants before safely exiting the pressurised environment.
What’s a Positive Pressure Room?
Positive pressure rooms maintain a higher air pressure inside than the surrounding environment. Air escapes the room without letting in outside contaminated air. PPRs exist within surgical theatres and in vitro clinics where contamination is possible. PPR hospital rooms often house immunocompromised patients susceptible to infection or disease. Because PPRs form barriers to outside spaces, their HVAC systems must filter out any contaminants from the interior air while ensuring optimal pressure and safe air quality.
Air Tightness
Pressure room designers try to keep rooms as air tight as possible, but some leakage occurs through gaps in doors, windows and electrical outlets. Designers often outfit NPRs with ante rooms to minimise leakage. These entryways are also safe areas for removing PPE or as a failsafe against pressure loss. Airtightness is also a cost issue. The more leakage, the more energy required to maintain a room’s negative or positive pressure.
Air Comfort
Like any conditioned environment, pressurised rooms must also maintain humidity and air temperature to ensure comfort and safety. Air quality is particularly important for medical facilities, since suboptimal humidity levels can contribute to illness. To aid air quality, HVAC technicians design HVAC systems to include specific numbers of air changes per hour (ACH) based on the size of the room. ACH is a measure of how often air within a space is replaced every hour and is essential to combating contaminated, stale and unhealthy air.
Testing and Monitoring
Smoke tests are a common way to test the effectiveness of a pressurised room. They’re cheap and easy to administer, but aren’t continuous or highly accurate. During a smoke test, technicians create puffs of smoke next to known intakes like registers or under doorways. If the smoke flows inside or outside, then a pressure differential exists. The smoke just needs to move in the right direction. Electronic pressure monitors offer continuous, accurate monitoring, but they’re expensive to purchase and install. Still, accurate testing and consistent monitoring is the best way to maintain the effectiveness of a pressurised room. Inadequate or infrequent testing puts patients and others at risk.
Conclusion
The COVID-19 pandemic has extended the use of pressurised rooms to combat the disease. The idea has extended beyond the hospital room to include waiting rooms, triage, bathrooms and other areas that could contain contaminants or susceptible people.
While pressurised rooms are helpful for health care workers, patients and staff, they also present challenges to HVAC techs and facility managers. Expanding the number and size of pressurised areas in any building means paying more attention to resulting issues like high humidity levels, sticky entryways, mold growth, and increased energy costs. These are new challenges FMs and engineers will need to address as the built environment evolves to meet social change.
Counting every kWh your property uses is important for your NABERS Energy Rating assessment. The more detailed your records, the more accurate your rating will be. Getting a true picture of your energy consumption means including and documenting your after-hours air conditioning (AHAC) service.
The NABERS Preparing for Office Rating Guide is a helpful resource for identifying what basic information to gather. But the guide doesn’t get into the specifics around documentation for AHAC. Documenting AHAC hours can be tricky given they’re usually tracked separately from normal operating hours. For a deeper dive, we recommend the NABERS Energy and Water for Offices Rules v.5.1. Although this resource is as a guide for assessors, it also provides valuable insights for FMs and property managers.
The Rules around AHAC are complex and hard to drudge through, so we’ve done the work for you. Below is a breakdown of the NABERS Rules for documenting AHAC, which will better prepare you for your assessment.
Rated Hours
NABERS assessors calculate the total number of hours per week your building is occupied—your rated hours. Assessors use your rated hours along with your annual kWh usage and other factors to determine your efficiency rating.
To calculate your rated hours, assessors will look at your core hours. These are your normal operating hours per week (e.g., 8 am to 6 pm). Core hours are usually listed within the owner/tenant agreement (OTA), and the assessor will likely use your OTA to help determine these.
To increase accuracy, assessors also include any AHAC hours. Your HVAC system uses energy to produce the AHAC service, so you should count these hours too. Any missing AHAC hours skew your total rated hour count, lowering your NABERS rating. And the impact will be proportionate to the total hours demanded. That is, the more AHAC hours omitted from your rated hours, the more inefficient your property will appear.
AHAC Documentation
The negative impact of omitting AHAC hours is why it’s critical to keep accurate logs of tenant requests. For NABERS, not just any records will do either. Assessors must deem data “acceptable” or else include it in the calculation. The NABERS Rules lists the following types of “acceptable data.”
Tenant Requests
Section 5.3.3.1 of the NABERS Rules addresses AHAC requests and states that “acceptable data” includes:
Logs of AHAC requests by tenants, showing the date and time of each request and the functional space to which it applied; and
Evidence of other AHAC requests, such as correspondence between the tenant and the owner or building manager or information written into the OTA which has been verified to be correct and up-to-date. This evidence must include the date, time and space to which AHAC has been agreed to be applied.
Therefore, an example of acceptable documentation might be an automated entry from an after-hours HVAC app that records date, time, floor and tenant. Unacceptable documentation might be a tenant email listing only the requested date and time. The most important part of accurate documentation is the tenant’s request, so keep this in mind when setting up your request process.
Overlapping Hours
To be considered rated hours, AHAC hours also can’t overlap with your core hours. So you’ll need acceptable documentation showing their separation. Section 8.3.2 of the Rules explains that to include AHAC hours, you must provide:
Evidence that no AHAC has been counted during the Core Hours and during the plant start-up period or the hour before the start of Core Hours if the plant start-up period is unknown;
One thing to note here: NABERS focuses heavily on counting only “comfort condition” hours— times when internal temps are appropriate for occupancy. Assessors assume that comfort conditions are not met during the start-up time for your plant. For that reason, you can’t count any AHAC hours that occur during start-up times for your system. If you can’t provide evidence of the actual run up times for temps, assessors will assume one hour.
Example: Your OTA lists your core hours from “8 a.m. to 6 p.m.” Your normal plant start-up time begins at 7 a.m. to reach comfort conditions. Tenant A requests AHAC from 7 a.m. to 8 a.m. on Wednesday, but your start-up time for Wednesday stays at 7 a.m. (i.e., AHAC and start-up begin at the same time). Since your building isn’t at “comfort conditions” by 7 a.m. on Wednesday, you can’t count that AHAC hour towards your rated hours.
Zones and Functional Spaces
To calculate AHAC hours, NABERS assessors also need to divide your net lettable area (NLA) into functional spaces— specific areas of your building. Functional spaces can be based on tenancy distinctions (i.e., leases) or physical ones (e.g. HVAC zones), but variations often happen. For example, multiple tenants could occupy the same functional space by leasing the same floor. In contrast, a single tenant might occupy separate functional spaces.
Regardless, the goal of defining functional spaces is to group areas with the same periods of occupancy so assessors can calculate the effects of vacancies and different operational hours on your building’s efficiency.
For facilities managers, the important thing to note is that AHAC requests need to reference their correct functional spaces. This is especially important when multiple tenants share the same functional spaces. Accurate records and detailed building schematics are essential, and assessors will use them to calculate your rated hours. To this end, Section 8.3.2 of the Rules requires documentation in the form of:
Drawings and measurements showing AHAC zones for requests serving different zones within a single functional space.
If the NABERS assessor can’t locate detailed areas for different AHAC zones, they will use the smallest area available or else average hours together. Either way, any guesswork will lower the accuracy of your rated hours.
The rules around multiple tenants sharing functional spaces and zones can get quite complex. So, read section 5.3.3 of the NABERS Rules to see what situation fits your properties the most.
Conclusion
The way your NABERS assessor handles your AHAC consumption will depend on several factors. One of those is how they arrive at your core hours. There are several methods for doing this, which depends on what data you make available. The assessor may determine your core hours from your lease. If data is missing, they may need to calculate an average, and when estimates are involved, you can bet they won’t likely benefit your rating. In the end, the key is proper and thorough documentation of your AHAC requests, HVAC zones, and NLA.
Definition: After-hours HVAC is the delivery and maintenance of a facility’s heating and air-conditioning services, outside regular operating hours, for the benefit of a tenant. Tenants pay an hourly rate (usually specified in a lease) for any costs associated with after-hours HVAC operation. After-hour times normally include evenings, weekends and holidays.
After-hours HVAC goes by different names in different markets. For example, in the U.S. it’s sometimes referred to as “overtime HVAC.” Some landlords may use the term “after-hours air conditioning” in a lease or shorten it to “after-hours air con” or “AHAC.”
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AHAC: A Response to Changing Workplaces
Social and technological forces have changed the workplace over the last decade. Millennials are now the largest generation in the U.S. workforce. AI and automation are driving increased productivity. The Internet of Things (IoT) is fueling smart building design, and the COVID lockdown kickstarted a revolution in remote working. The standard 9-to-5 work day is behind us, replaced by hybrid schedules, teleconference meetings, and a more remote workforce.
These social and technological changes accelerated specific trends within facility management and building design. These include a move to more flexible workspaces, the integration of “smart” tech and the push for sustainable design. It is out of this demand for more work and building flexibility that services like after-hours HVAC emerged.
Today it’s commonplace in the FM industry to provide tenants with lighting and HVAC services outside of normal operating hours. In turn, firms use this flexibility to expand work hours, hold company meetings and host special events.
Charging for AHAC
Usually the first question a property owner asks is “How much do I charge?” Most tenants and/or their lease advisors insist that AHAC charges represent a reasonable estimate of the “actual cost” for providing after-hours service. But what is the actual cost of operating an HVAC system for one hour? Calculating a “reasonable” estimate is often difficult because HVAC systems are complex. In addition to electricity, they also require water, gas or oil to operate. Then there’s wear-and-tear of equipment, staffing, elevators, car parks and other costs to consider.
To keep things simple, some FMs determine a fixed rate based on the electricity, depreciation and a small percentage to cover “admin” costs. Other landlords avoid the hassle altogether and include the estimated cost within the monthly rent. While there are AHAC calculating best practices, the best approach is one that balances accuracy with simplicity.
Billing Strategies
Billing tenants for AHAC takes several forms. Most property managers start the billing cycle the day they execute the lease. AHAC hours are charged at the agreed rate and billed to the tenant if and when they make a request. Other FMs may allot a number of free overtime AC hours for the term of the lease (e.g., 300 hrs for 5 years). In that instance, an AHAC charge begins only when the tenant exceeds those cumulative free hours.
FMs can bill tenants for AHAC on a monthly, quarterly or yearly basis. After-hours HVAC charges are always billed separately from normal operating hour utility expenses to avoid double charging tenants.
Lease Stipulations
Lease stipulations are common within AHAC tenancy agreements. Some lease clauses may further define AHAC times by listing specific holidays or “dates of observation.” Other provisions set limits on tenant usage to protect the landlord against unexpected costs. For example, most property owners include a provision that allows an annual review and adjustment of AHAC rates based upon current utility costs. This is to protect the landlord against the volatility of energy prices.
To assure quality service, the majority of leases also require that tenants give a 24 or 48-hour notice. The stipulation ensures engineering staff have enough time to carry out the request. There’s also a practical reason. Every HVAC system requires a start-up time to bring the property to the standard temperature (e.g. 22°C/72°F). Notices help give the system enough lead time to ramp up. Start up times are also why landlords stipulate a minimum service time of one hour. Scheduling the HVAC system for only 30-minutes wouldn’t likely cover the actual cost of operation.
Scheduling
There are several ways to request AHAC services. Many programs have tenants create a work order or similar request via a tenant portal. Maintenance staff then program beginning and ending times along with the dates requested. The tenant then arrives at the property on the scheduled day and time.
Other properties equip each floor or tenant space with its own controls, usually a switch or button-operated interface. Occupants have control and can “order” after-hours AC or heating simply by turning the system off and on. Software then records the time and duration and charges the tenant accordingly.
Forward-looking facilities use after-hours automation software that give tenants more control of the scheduling process. Tenants make their AHAC requests through a smartphone app or web browser. The software then programs the system to operate at the desired time, date and duration. These programs cut down on staff time and increase scheduling flexibility.
If you haven’t yet automated your after-hours HVAC program or, worse, have no program at all, you’re missing out on benefits that maximise your staff productivity and cut out wasted time. Automation also helps increase tenant satisfaction and productivity, which, in the end, helps your properties thrive. Here are the biggest benefits from automating your after-hours HVAC program.
1. Easier Scheduling
The typical after-hours HVAC scheduling process usually involves several staff members and these four steps:
Tenant fills out a work request in person or on the website portal
The request is recorded on a spreadsheet
The building engineer programs the request into the HVAC system
The facility manager prepares & sends monthly billing statements for each tenant
Each step requires time and resources from your team, and when problems pop up, tasks grow exponentially. If an engineer isn’t available, another staff member has to be scheduled. When a tenant needs to schedule a change, someone must sort things. An AHAC cloud-based platform eliminates these issues by automating many of these manual steps. Here are the steps in an automated system:
Tenant makes a requests via smartphone app or desktop browser
(Automated) Recording requests entries
(Automated) Programming the HVAC system
(Automated) Sending monthly statements
Automation reclaims lost time from tending to tedious tasks. You can, instead, spend that time improving your property and tenant experience.
2. Fewer Billing Errors
By eliminating steps in your after-hours HVAC program, you stamp out inaccuracy. The best-laid plans run into the realities of everyday life. Engineers get sick. Requests are forgotten. Entries are flubbed. Statements don’t match. In contrast, automation software doesn’t lie, get ill and or forget.
The fallout from mistakes isn’t just the wasted time setting things aright. For facility managers, inaccuracy means loss of profits, and those losses can be huge.
When a billing discrepancy arises, it’s often easier to acquiesce than upset a tenant. Some managers avoid charging for after-hours at all because they fear situations like this. Where this is the case, you’re unnecessarily paying for another business’s electrical costs while shortening the life span for your HVAC equipment. The accuracy of an automated after-hours program ensures your properties stay profitable.
While AHAC automation may seem like a simple tool, its potential impact for FMs and their tenants is limited only by the lack of exploring its many applications for both.
3. Happier Tenants
Most automated after-hours platforms let tenants make reservations from a smartphone app or desktop browser. It’s a perk that benefits both managers and tenants. Tenants no longer need to waste time filling out work requests, and managers can reduce staffing costs associated with after-hours management. Since AHAC apps fully integrate with your BMS, start and stop times for HVAC service are automatically received, executed and terminated by the software. This frees your engineers and maintenance staff up to attend to higher property priorities.
Since lease holders can schedule after-hours HVAC “on demand,” this eliminates the need for an advanced notice. Most commercial leases with an after-hours clause stipulate a 24 to 48-hour advance notice from the tenant. But tenant schedules can vary wildly. Some have highly predictable office hours; others manage chaotic itineraries. For the latter, even a 24-hour notice puts them in a tight spot. But by eliminating the need for a notice, automation apps give your tenants and their employees greater work flexibility — a growing priority for workers splitting their work hours between home and office.
4. More Sustainable Properties
Going on-demand with your after-hours HVAC program conserves energy to. Changing or canceling bookings by mobile device is easy and convenient for your tenants, so they’re much more likely to cancel their after-hours appointments when things change. The upside is you won’t be heating or cooling empty properties simply because something came up at the last minute. With more accurate billing, you’ll get a better overview of your total energy use and be able to find opportunities to increase efficiency and cut waste.
Pro Tip: Identify seasonal trends for your after-hours program and use the data to make targeted improvements in lighting, insulation or renewable energy investments within specific zones of your property.
Conclusion
The benefits of after-hours HVAC automation make a strong case for its adoption among facility managers. While it frees your team from tedious tasks like reporting and billing, automation’s biggest selling point is it’s a value-add for your tenants.
Clients and their office managers can use the data collected by automation software to streamline their own internal processes. Retail tenants can use after-hours data to set sustainability benchmarks and goals. Software developers could employ after-hours usages in evaluating each team’s productivity and/or cost to a project. Law firms could recoup losses by adding their AHAC charges as a billable line item for a client.
While AHAC automation may seem like a simple tool, its potential impact for FMs and tenants is limited only by the lack of exploring its many applications for both.
If you’re new to after-hours air conditioning (AHAC), you may find it hard getting started drafting a lease or tenancy notice. AHAC is a complex topic, and each property requires a bespoke solution. However, there are a few basic terms and ideas that appear in most agreements regardless of your circumstance or location. While you should always consult a legal professional when drafting leases, the following tips and topics will help get the ball rolling.
Define “AHAC”
To start, make sure you have a clear and unambiguous definition of after-hours AC. Ensuring accuracy and clarity in your leases not only covers you legally, it helps improve tenant satisfaction. Use a term that’s common for your area. In some markets, after-hours service is referred to as “after-hours HVAC” or “overtime HVAC.” Other times a lease may only refer to it as “after-hours air con” or “AHAC” for short. With a little research, you can locate the preferred name for your situation. But regardless of the moniker used, be consistent to avoid confusing your tenants.
Next, your definition needs to set parameters for when AHAC applies. In most situations, it refers to charges incurred by any tenant who operates the air conditioning system outside of normal operating hours. Therefore, your definition must necessarily include an explanation of “normal” operating hours.
List Normal Hours of Operation
the core operating hours for a property are usually stated within the lease, but it’s a good practice to remind tenants in all your communications. Use a simple table like the following that clearly lists times and days for each floor, tenant and/or zone of the property.
Level 2
Mon-Fri
8:00 am — 6:00 pm
Saturday
8:00 am — 1:00 pm
Level 1
Mon-Fri
8:00 am — 6:00 pm
Saturday
8:00 am — 1:00 pm
Ground
Mon-Fri
9:00 am — 5:00 pm
Saturday
9:00 am — 12:00 pm
Example of table listing core operating hours.
By definition, any HVAC usage outside of normal operating hours is considered AHAC and will be charged as such to the requesting tenant. In contrast, you could list a table showing only times that fall inside the AHAC time slots, if this makes it easier to understand.
Remember to mention any specific days outside the scope of operating hours such as holidays. And if you don’t plan to make AHAC available to all parts of your property, then list those excluded areas in your lease and/or communications with tenants.
Explain Fixed Rate Calculation
Explain how you calculated the energy costs (i.e., fixed energy rate)that factored into your after-hours HVAC fee. If it was based on an average energy cost across the entire property for a specific time, then show how you prorated the amount. Maybe your energy provider calculated the hourly cost for you. If so, briefly explain how this process works. If you estimated the hourly energy based on the equipment involved, then list these HVAC assets for the tenant. Such assets might include chillers, AHUs, VAVs and FCUs.
Yes, your tenants are likely to have little interest in how air handling units work. But they will appreciate that you’ve done your due diligence in calculating the actual energy expenses for which you’re charging them. Such reassurance is beneficial when billing issues surface.
Add Excluded Costs
You may also want to list any excluded HVAC equipment or service costs. These can include anything within your fixed energy rate calculation that you’ve chosen not to include even though it’s an actual operating expense. For example, your chiller uses water for heat rejection, but it may be impractical or impossible to get an accurate measurement. Therefore, you may end up omitting water usage from the fixed rate calculation. Other omitted costs often include electricity for lighting hallways, car parks and powering elevators.
An excluded equipment and services list may seem like overkill, but it does show tenants you’ve chosen to absorb some of the costs. This can help quell future complaints about AHAC increases.
Show Tenants How to Calculate AHAC Charges
Finally, write out the actual formula for calculating the AHAC monthly charge. Examples clear up the process for your tenants. At minimum, your AHAC charge will include the following elements:
Fixed Rate x Number of Operating Hours = AHAC Charges
At this point in the lease, record the amount of the AHAC hourly charge (e.g., “$75 per hour”) Examples here are helpful too: “Tenant A used 10 hours of after-hours HVAC for the month, their total charge would be $75 x 10 = $750.”
Accelerated Depreciation
Including wear-and-tear of your HVAC equipment helps offset replacement costs for their shortened service life. If you include accelerated depreciation in your fixed energy rate or AHAC charges, add it to those sections as a line item or as part of the AHAC formula. There are many ways to recoup depreciation losses. Some property owners make depreciation a separate charge, adding the fees to a general “building fund” that goes to maintain the property as a whole. Whatever method you choose, justify your decision by pointing out that after-hours HVAC operation shortens the life-span of your equipment. You’ll need those funds for PPM and to ensure a comfortable building environment for tenants.
Fixed Rate Adjustments
Electricity costs fluctuate, and so will your fixed energy rates. To stay profitable, many firms add a 12-month fixed rate agreement to their lease. The agreement stipulates that when the year ends, the fixed rate will be reviewed and adjusted according to current market rates. Including a section in your lease that explains your rate review strategy helps tenants avoid sticker shock. Email reminders at the beginning of the year also prepare tenants for rate increases.
AHAC vs Annual Operating Expenses
Keep after-hours HVAC charges separate from your annual operating expenses. There’s the potential that AHAC kWhs are accidentally mixed with your normal end-of-year utilities bill to tenants. If this is the case, you will end up charging tenants twice for the same energy usage.
Savvy tenants will anticipate this possibility of energy “double-dipping” and want reassurance from you. Prepare for these concerns by explaining that you’ve taken measures to ensure accuracy and fairness in your billing. It’s the most effective way to avoid confusion down the road.
Conclusion
It’s clear there are many factors to consider when building an after-hours HVAC lease agreement. In the end, you can make a lease as simple or complex as you like. Your approach will ultimately be guided by how much time you want to spend vs how much energy costs you want to recoup. The more accurate your fixed rate calculation, the more research it will require. For some, the time spent figuring excluded costs may not offset the benefits of avoiding tenant complaints. But most managers will adopt an approach that prioritizes tenant satisfaction. Eating a bit of operating expenses is a small price to pay for full occupancy and happy tenants.
