Winter is coming for most of us in the northern hemisphere and that means it’s time to perform some last-minute maintenance checks on your HVAC system. Here are some maintenance items to check to prevent later, larger issues.
• Determine what isn’t working prior to needing it: Test your heating system now to find issues before it’s too late! Bump up your temperature setpoints, place your units in test mode, or fake out your outdoor air temperature sensor with a bag of ice. Run your building through its paces now.
• Freezestats: These are installed to protect your precious coils so you don’t have to! Make. 100%. Sure. They. Work. It’s not as simple as hitting a button because during install the copper tubing holding the temperature sensitive gas can be compromised. How to test?
1. Make sure they are installed in the correct location, directly downstream of the hot water coil (upstream of your cooling coil) in a horizontal serpentine fashion spaced evenly across the coil. This location will prevent false trips and provide full coil coverage.
2. If the freezestat comes with an adjustable temperature setting, set the temperature as low as you feel comfortable with, without dropping below freezing (35F is typical).
3. Buy freeze spray or ice and physically apply to 12”-18” of the serpentine copper tubing which holds the temperature sensitive gas vapor. The gas vapor pressure will drop and cause the freezestat to trip.
4. Verify sequence of operations resulting from a freezestat trip occurs. Typically this will include a shutdown of unit fans, closing of the outdoor air damper and an opening of the hot water valve.
5. To reset the freezestat you may need to both physically reset the freezestat using the button on the control box as well as clear any front-end alarms which have been programmed to prevent the unit from automatically restarting after a freeze condition.
• Filters: Are you keeping up on your filter changes? If you are changing on a schedule or using filter differential pressure monitors to report filter condition to your building monitoring system (BMS), it’s a good idea to physically check your filters this time of year. Clogged or weather dampened filters can cause your unit to provide less BTUs of heat than designed.
• Coils: Similar to filters, a dirty coil can cause your unit to provide less BTUs of heat than designed.
• Outdoor air dampers: Physically verify that your outdoor air dampers are actuating open and closed as required. If your dampers are tough to access, monitor the mixed air temperature at the front end after commanding the damper open and closed. If the damper is working, the mixed air temperature sensor will reflect that.
• Outdoor air temperature sensors: Verify your outdoor air temperature sensors remain accurate. Most likely, your boiler relies on this temperature to decide how hot your hydronic system needs to be. Your air handling units use outdoor air temperature to help decide if economizer mode is applicable or not. In both situations, an accurate outdoor air temperature saves you money and headaches.
• Condensate drains: Check your condensate drains and verify they are clean and clear of debris. Afterwards, pour some water down the drain and make sure it works. In cold climates with rooftop units, insulation and heat tape may be required to keep these drains from freezing so your units can keep on running.
• Check piping insulation: Did you replace some piping over the summer? Make sure your piping insulation remains intact and complete.
• Winterization: Make sure you properly have winterized your cooling systems prone to freezing. If in doubt, check your O&M manual.