Two Speed RTU Economizer Update
Two Speed Blowers:
As of January 1, 2018 the US Department of Energy mandated that all Roof Top Units (RTUs) six tons and heavier must have a two-speed blower to achieve Integrated Energy Efficiency Ratio. Existing RTU inventory manufactured prior to 1/1/2018 with a single speed blower can still be sold until inventory is gone.
The two-speed blower requirement will be accomplished by utilizing a single-speed belt drive motor and controlling it thru a Variable Frequency Drive (VFD). The VFD will be factory set with two digital control inputs. The first stage cooling fan will be at 66% of blower speed, while the second stage cooling fan will be at 100% of blower speed. Heating will be at 100% blower speed while ventilation will run at 66% of blower speed.
Air balancing will not be done by adjusting the VFD, as it will not be supplied with a keypad, and will be factory set. Air balancing will be accomplished by jumping the yellow and black leads together (located near the blower) and adjusting the blower motor sheave as is normally done.
New energy code requirements mandate that the economizer dampers are of a low leakage design. With the two-speed blower motor, a two-position minimum damper control is required. All two-position economizers will be supplied with the Honeywell JADE economizer control. The wiring and installation of the Jade control is simplified and the harness is supplied in the RTU.
The control itself will be mounted in the main control compartment; it will no longer be mounted on the economizer. The Jade control has fault detection and a simple check out with an onboard display. Enthalpy control utilizes separate temperature and humidity inputs, giving a much better change over from free to mechanical cooling. In most cases, enthalpy is preset in the factory so no further adjustment will be required. This means there is no more A, B, C, and D setting. Simple set up of minimum position, demand ventilation and enthalpy (when required) are accomplished utilizing the on-board display on the controller. An installation video can be viewed by utilizing the QR code located at the top of this page.