Everything About HVAC Is Flow
3 Min Read By Richard Boothman
With the advent of COVID-19, there have been plenty of questions about ventilation and how it can improve interior spaces by making them safer. Tips include: not bypassing or disabling the energy recovery system; breaking down interior spaces to decrease contamination; ionization kits applied to equipment; and maintaining a higher pressure in the supply air section than the exhaust air section, to name a few. Designers are also looking at more advanced filtration systems, which are in the process of becoming more sophisticated and more expensive. A filter with an efficiency of MERV 13 can be very effective. While COVID-19 is responsible for massive disruptions, it will also generate its fair share of innovation.
Everything about HVAC is flow. Without good flow, the unit runs longer and harder, and when it does, efficiency and ventilation will suffer. Keep the system maintained and in great shape. Don’t be afraid to invest in a new piece of add-on technology. And keep the building properly pressurized. If these basic steps are taken, it might be 90 degrees with 75-percent humidity outside, but it will feel like a comfortable spring day on the inside. And with a big night of service on the reservation books, that’s a good place to be.
Keeping the heat and humidity out of a restaurant during the spring and summer is not easy. Patrons and employees expect a basic standard of comfort, and if they can’t find it in one establishment, then they will find it in another.
The trick is that the 72-degree day with low humidity, at least in many places, does not come around that often, if ever, in July and August. But inside the restaurant, it’s supposed to feel that way, even if it’s 90 degrees outside. and the air is heavy with moisture.
Restaurant owners, of course, should know the rhythms of the seasons and be prepared to properly ventilate their buildings during the summer months. They must also consider the hallmarks of the hospitality trade — heavy foot traffic, the opening and closing of doors, and the massive heat and exhaust generated by a kitchen equipped with a grill, fryer, oven, dishwasher and cooler. A lot of air is pulled into a restaurant, and a lot is pulled out. A great ventilation system is a must.
So, what does that look like? For starters, precautions have to be taken at the design phase.
An important step is to ensure that the building is pressurized so that the system is not pushing out more conditioned air than it’s pulling in. Set the volume of the unit, the volume of the extraction and the exhaust and then make sure those settings are maintained. Leakage isn’t good for efficiency or ventilation. Modine units can monitor building pressure and adjust fan speeds through a variable frequency drive, (VFD).
With issues taken care of at the design level, it’s time to think about maintenance. A good restaurant owner will have their HVAC system inspected seasonally, at the beginning of the spring and at the beginning of the winter. The checklist should be long and extensive and cover every aspect of an HVAC system: filters, belts, vents, refrigeration system, electrical connections and components, and the gas supply and pressure settings. Without semi-annual inspections and preventive maintenance, there will be more to worry about than ventilation on a hot and humid day. The system could fail at the most inopportune time, forcing a restaurant to close its doors while a costly repair is made.
During any inspection, it’s important that recent weather is taken into consideration. Did a snowstorm damage anything? Did that thunderstorm that blew through town knock something loose? Sheet metal, fans and air movers, wiring, piping and vents are all at risk during violent weather events.
When it comes to ventilation, there are a couple of things a building owner can do that will not only improve ventilation but could produce savings through efficiency. One way to deliver quality air at room temperature is to have a deeper coil. The outside air remains in the coil longer and is dehumidified. That air also cools down, so it needs to be reheated a bit before being sent into the building at room temperature. A hot gas reheat coil using redirected condenser gas will accomplish this without requiring additional energy.
Another useful thing to do is to decouple the outside air ventilation load from the space load by installing a Dedicated Outside Air System, (DOAS). This can help reduce energy consumption. These systems focus purely on the outside air load so the terminal units and space conditioning units are able to focus only on the interior.
And don’t forget about installing the right size of HVAC in the first place. Oversizing one can be a problem in cooling as, without modulating control on the compressor, the unit will simply not run long enough to dehumidify the air. On a typical summer day, oversizing results in a cold and clammy room, which isn’t good for patrons or employees.