Not only does this process give the manufacturer some security, knowing that they’re sending out a product that works, the contractor can feel better knowing that someone has already given a particular rooftop unit the once-over.

What does a contractor want in a rooftop unit? Not just performance to meet customer expectations, he’s also looking for a product that is easy to install and maintain. The less time and labor a contractor has to spend on a particular job, the more jobs the contractor can get to that day.

Saves Time, Costs

Contractors are a vocal bunch when it comes to making clear their needs and expectations of rooftop units. York International believes it has responded to their concerns. In essence, this manufacturer is trying to make things simpler for contractors. This has included using a central terminal strip connection for any hard-wired inputs that reside in the panel.

“We have a ddc microprocessor board toward the back of the control panel that is located beneath the display. The terminal strip allows for real simple control and connection to the unit — thermostat control, sensor control, that kind of interface. Then if communications are required, we offer a BACnet interface for the customer to tie the rooftop into their building automation system,” says Brian Smith, product manager, York.

Smith adds that the company has focused on the BACnet protocol, as it makes it easier for contractors to tie a rooftop unit into a building’s automation system.

“It’s not a proprietary control — it’s open and everyone has access to it, and it doesn’t lock out certain types of systems,” he says. “There’s always going to be some interfacing that has to be done.

“But if it’s interfacing to one standard from a variety of different protocols, it’s easier than from a variety of protocols to a variety of protocols. We’re minimizing the number of combinations. If you’re always trying to make that interface to one language, it makes it easier,” says Smith.

Installed at the factory

At York, the microprocessor ddc board, as well as all the sensors, switches, and valves in the rooftop unit, are installed and completely wired in the factory. At the end of the production line is a tester that connects through the communications port on the ddc board and tells the unit which options are installed on that particular unit. That way, the controller knows which sequences to run.

Then the tester makes the rooftop run through all of its operations to make sure the components are working properly. For example, it will turn on the compressor to make sure it’s drawing the right number of amps, and it will turn on the fan to make sure it’s working properly before leaving the factory. Then the entire rooftop unit is shrink-wrapped before it ships, so it comes out as one nice package.

“Installing, testing, and commissioning all the controls in the factory helps the contractor from the standpoint that he doesn’t have to install any controls; he just has to make connections. That minimizes the amount of labor that a contractor has to put into a project. The additional time it takes is money for him,” says Smith.

It also makes sense that it would be easier for a manufacturer to install the controls at the factory rather than a contractor doing it out in the field. In a factory the rooftop unit is built from the ground up, so there are no panels, doors, floor, or roof. That makes it much easier to run all the control wiring and mount the controls in the unit because it’s not enclosed.

If the contractor wants to install something additional at the jobsite, the rooftop is already completely built up, so he usually has to pull out a drill or a saw and start cutting through things. As soon as that happens, the integrity of the product is violated. Not only does it become possible to cut through something that shouldn’t be touched, it’s also possible to have leaks if the unit isn’t sealed properly afterward.

Even if the controller fails, all that needs to be done is to remove some wiring. Then the board can be disconnected and a new board put in. Of course, the contractor needs to make sure the configurations are set correctly. But beyond that, not much tinkering needs to be done.

So, is there ever a time when controls should be installed in a rooftop in the field? Smith can’t think of any.

“There are always exceptions,” he says. “Sometimes things are done in the field that are outside the normal scope. But we’re trying to make the rooftop a simple product to work with. All the control sequences are resident in the controller; you just configure them and it minimizes the programming time and the set-up time on the product.”

Publication date: 06/25/2001