Reduce Excess of Air Flow
Most rooftop HVAC systems (over 90%) run at a constant volume. Because the fan is on continuously and the compressor only intermittently under most conditions (no matter what the occupancy is and no matter what time of day), in many locations the fan energy consumption can be greater than the compressor energy consumption.
Although there are a number of hours during the day when a building may not be fully occupied or the need for ventilation is lower than designed, the ventilation rate cannot be adjusted easily with a constant speed fan.
Retrofitting packaged HVAC units
The inversion cost of retrofiting an existing rooftop HVAC unit with advanced controls like the RTU-SC supplied by GreenmediaHD, is much less than installing a new unit, and once the retrofit is done, you can save from 35% up to 50% of energy, recovering your inversion in less than two years. Advanced control technology provides variable speed control, which means the rooftop unit only operates at the volume needed. A set of precision sensors are installed in the existing RTU to calculate the exact demand of flow of air.
If the evaporator coil is not cold enough, it cannot remove moisture, and it will stop removing moisture at its dewpoint temperature. The lower the airflow, the lower the evaporator coil temperature, so reducing fan speed to a proper value, reduces humidity.
Moisture removal can improve indoor air quality(IAQ) and occupant comfort, while supporting facility operations and maximizing the life of your building, furnishings and equipment.
Compressor work reduction
When the fan speed is reduced, the fan heat decreases and reduces building cooling load which make the compressor save energy in cooling mode. At high outside air temperatures, when the outside and inside air mixture is reduced by lowering the fan speed, the building cooling load is also reduced saving compressors energy. The level of carbon dioxide in the air can be monitored to keep a good IAQ.
How RTU-SC Works
Fan Speed Modulation
In RTU cool mode, the RTU-SC modulates the fan speed to a proper value while protecting the compressor and keeping a good comfort humidity value. To modulate the fan speed to a proper value, precision sensors are used to measure the parameters used in the optimization algorithms.
With the collected data, important parameters are calculated.One of these parameters is the superheat. Superheat occurs when refrigerant vapor is heated above its boiling point. Superheat is critical in HVAC because it ensures the liquid refrigerant is boiled off before it leaves the evaporator and heads to the compressor, and even small amounts of liquid can cause detrimental damage to the compressor in an HVAC system. RTU-SC set the fan speed to a value that guarantees that superheat is above 8oF and tries to keep this value in a recommended range (8oF-25oF). Others calculated parameters and sensors values are used to control the fan speed to maintain the proper indoor air humidity quality. Optionally, the levels of carbon dioxide in the air are taken in consideration to set fan speed. Finally energy consumption and energy reduction parameters are calculated to evalute the energy savings in real time.
For other RTU modes, the fan speed is indexed to a value configured by operative personal and recommended for the building location and environmental conditions.
How it is Done
One of the program modules of the RTU-SC deals with energy saving. Precise sensors are used to measure the current and the state of operation of the fan motor. When modulating the fan speed, the RTU-SC calculate the kw consumption and kw-h energy of the fan and compare those values with the nominal kw consumption for a constant fan speed (normally 60hz). The compressors kw consumption and kw-h energy are also calculated.
As a result, we get the reduced kw and kw-h of the RTU due to the speed modulation algorithm used by the RTU-SC.
The RTU-SC can be set to operate in evaluation mode to get the real savings. In this mode the optimization algorithms that modulates the fan speed are enabled only in even days and disabled in odd days. During the odd days, the fan speed is set to the constant nominal value which is the current value if not optimization is applied. Also, power meters are installed in the RTU to collect the kw-h energy consumption and compare both days. This evaluation is made for a minimum period of a 15 day.
The main goals of this evaluation mode are:
Get the real energy savings results
By comparing the energy consumption obtained the even days with the obtained for the odd days, the percent of energy savings for that particular RTU can be estimated more accurately. Reports are elaborated to show the real energy savings.
Report a real time saving calculations more accurately
The collected data is used to adjust the energy saving program module of the RTU-SC for a more precise result. This module shows in real time the energy reductions results in dashboard Web pages
Precise Sensors and Actuator
A set of precise sensors to get the best and reliable results in energy savings are installed to retrofit the existing RTU.
The main sensors includes: pressure sensor, temperature sensor, and current transformers.
Optionally indoor carbon dioxide sensor and power meter can be installed
A Variable Speed Drive (VSD) is installed to modulate the fan speed. The speed value is set by the RTUcontrol38 controller when the proper fan speed value is calculated to save energy during cooling mode of RTU. For the others RTU modes (heating and ventilating) the value of fan speed is indexed according to operational conditions of the RTU set by the maintenance operators.
This is the main controller of the RTU-SC and is used to modulate the fan speed to save energy.
This controller, supplied by Contemporary Control System, Inc., is programmed using Sedona Language. Six specialized program components where designed for this controller: fan speed controller, alarm supervisor, energy saving calculation, protection module, evaluation module, and schedule module.
Every RTU use one RTUcontrol38 and all the sensors used in the RTU-SC are connected to this controller.
This Gateway is connected via Bacnet IP in a local network with every RTUcontrol38 controller. The functions of the Gateway are: collect data from the controllers, send commands to each controller, synchronize date and time of all the controllers, send all collected data to the GreenmediaHD Web Server, and receive commands from the GreenmediaHD Web Server and transmit them to the target controller. The Gateway also has an embedded Bacnet IP Server that can be used to easily integrate all the RTUcontrol38 controllers with existing BMS.
GreenMediaHD Cloud Sever
All data is sent to the GreenMediaHD Cloud server to be visualized in customized Web Pages Dashboards.
Energy reduction reports are shown in real time allowing evaluate the everyday energy savings.
Commands like setpoints and schedules to each RTUcontrol38 controller can be sent from GreenMediaHD Cloud Sever.
GreenMediaHD Cloud Sever also shows a variety of alarms in each RTU and give some recommnedations on how to solve the issues that triggered them.
We install all the necessary sensors and the VSD in the RTU to modulate the fan speed and make energy calculations. Also the Bacnet IP communication network is installed to connect all the controllers to the Gateway.
Installation of the RTUcontrol38 and Logger Gateway
The RTUcontrol38 controller is installed in the RTU and all its parameters are setup for best results. This parameters are mapped into the Logger Gateway. This Gateway is also configured for optimum results for the characteristic of the target RTUs
RTU-SC Cloud Analytics
A user account is created in the RTU-SC Web Server to monitor and have some control of all RTUs anywhere you are. Evaluation and energy saving reports, and much more information about the RTUs are displayed in dashboards.
Bacnet IP server for Integration
The RTU Logger Gateway has a built-in Bacnet IP server which allows third party integrators of other building systems, such as existing BMS, to get all the parameters measured and calculated by the RTU-SC and also send back commands to the controllers.
Continuous update of the RTU-SC
Whenever a new software version is ready, the user can download it from the RTU-SC Web Server and install in the RTU Logger Gateway. Optional a VPN can be installed to remotely update every RTUcontrol38 controller when a new software version is available.
Consulting and technical support
We prepare the maintenance operators in campus to operate the RTU-SC by them self, and we also give support and recommendations to get the best energy savings results.