HILTON HEAD ISLAND, S.C. - The No. 1 and No. 2 complaints in almost any office is that it’s either too hot or too cold. This holds true almost everywhere, and it was especially true in the administration building of Providence Presbyterian Church.
Over the years, the nearly 3,000-square-foot building has been plagued with comfort problems. Very few of the church staffers were ever comfortable, except for the person in the center office - the one that had the thermostat.
This thermostat controls a 7.5-ton heat pump that supplies about 2,400 square feet of the building. The remaining four offices are supplied by a 3-ton heat pump, whose thermostat is located (where else) in the hallway outside of these offices, with the return inlet just above in the ceiling.
As is typical with most offices, as well as in homes, no one occupies the hallway. Yet the thermostat typically seems to end up there. Why? The answer, according to Zonefirst president Dick Foster, is because nobody ever considers zoning the system, so each office or zone can have a thermostat. “Those who design and lay out systems still do not consider zoning each room, office, or zone,” he said.
When the 3-ton unit died at Providence Presbyterian, the first instinct for Dave Miller of Superior Heating & A/C, Bluffton, S.C., was to change out the 3-ton unit. But while walking through the offices on a design temperature day with Foster, and considering that the areas served by the 7.5-ton unit were all at about 72°F (which was where the thermostat was set), Foster pointed out that they didn’t need to replace the unit. Instead, they could shift some of that 72° air over to the offices served by the 3-ton unit.
A BETTER WAYWhen looking at the attic space above the offices, Foster observed that all of the ductwork was easily accessible, and the 3-ton unit was only about 10 feet away from the supply and return ducts of the 7.5-ton unit.
The church could save some money by removing the 3-ton unit, connecting the supply and return plenums to the supply and return trunks of the 7.5-ton unit, and installing zone dampers in the duct for each respective zone.
A total of nine dampers were used on six zones. Two rectangular dampers were inserted into the top of the ductboard, with one controlling the library and restrooms, and the other the reception area, conference room, and an office.
So after years of being at the mercy of his secretary, who had the main thermostat in her office, the pastor finally got his own thermostat to control both of his offices. The secretary gets to keep her thermostat, and the associate pastor gets his own thermostat as well. Lastly, the music director and youth pastor in two of the smaller offices served by the 3-ton units now have a thermostat to share for their offices.
The thermostats used for the five new zones are all programmable and wireless, which saved a lot of installation time by not having to snake the wires through walls, Foster said. “The existing thermostats were not even programmable, so if someone forgot to set the thermostat back at night, there wasn’t much energy saving going on.”
ACCOMMODATING HOURSPeople who have not worked in a church may not realize that a lot of activities go on at widely different times of day. After interviewing the staff, Foster and Miller learned:
• Almost everyone had staggered hours.
• Each thermostat would be programmed for varied times, stretching the capacity of the 7.5-ton unit even further.
• The library, one of the single largest rooms, was rarely ever used, and when it was, those in the library were not in their offices.
In addition to the ducts added to connect both the supply and return of the old 3-ton unit to the 7.5-ton ducts, a 14-inch bypass duct was added to connect the supply to the return on the 7.5-ton unit. This duct has a modulating damper controlled by a static pressure sensor in the supply duct. When the static exceeds 0.3-inch wc, the bypass will open to relieve the excess air into the return. The damper will modulate open, then close when the static changes as the various zone dampers open and close.
The moral to the story is that “Simply changing out a failed unit may provide the occupants basic heating and cooling, but it would not have solved the main problem: The church staff was un- comfortable,” Foster said. “Not only has zoning made them comfortable in each office, it’s also provided for a substantial reduction in the capacity [tonnage] of the HVAC equipment.”
Many older systems have been oversized, he said, “and in this case extra units were added to ensure there was more than enough capacity.”
Also, it’s important to not only look at the total system, but also to talk with those who live or work in the building and consider their comfort. “There’s a light switch for every room or office,” said Foster; “why not a thermostat? When you consider that 40 percent or more of most buildings’ energy use is for HVAC, zoning makes sense. Studies have shown that zoning saves energy, as much as 30 percent.”
In this instance, zoning solved the overall comfort issues and cost the church about the same as replacing the existing unit would have. The savings and added comfort outweighed the decision to replace the second unit. In this instance, in fact, zoning the air distribution system allowed them to downsize system capacity.
For more information, visit www.zonefirst.com.
Publication date: 09/27/2010