Reduce Chiller Lift
The most energy losses in a chiller is excess lift. Lift is determined by subtracting the temperature of the chilled water going out to your building from the temperature of the water that’s leaving the condenser to be cooled by a cooling tower or fans. The term lift can also be used to describe a chiller’s operating pressures in place of its temperatures.
Chilled water reset strategy to reduce Lift
The leaving chilled water temperature was traditionally fixed, usually somewhere around 44°F. The chilled water reset allows the temperature of the chilled water to be increased during part load conditions. This reduces the amount of work done by the chillers compressor.
Compressor work reduction
The increase in chilled water temperature results in an increase in evaporator pressure of the refrigerant. The compressor takes the refrigerant at the evaporator pressure then compresses it and increases its pressure to the condensers pressure, so the higher the evaporator pressure the less work the compressor needs to do to increase that pressure.
How GCOP Works
LCHWT Setpoint Reset
The GCOP optimizer controller is connected via Bacnet IP to the chiller control panel and resets the leaving chilled water temperature (LCHWT) setpoint in real time to an optimum value. To calculate this value, the GCOP starts learning the behavior of the chillers during different cool loads. The data used in this learning are: the ambient temperature, the entering chilled water temperature, the current leaving chilled water temperature setpoint, and the current chiller capacity. With this data, the control function is based on 4 basic components:
At a lower outside temperature, the setpoint can be increased and vice versa.
Current Cool Load
The cool load is proportional to the difference between the entering chilled water temperature and the leaving chilled water temperature setpoint. The setpoint value can be increased for lower cool load
This value is also proportional to the cool load and can define the magnitude of setpoint reset value.
Space Room Temperature
One or multiples space zone temperatures are monitored to limit the setpoint increased value.
Once evaluated the magnitude of the incidence of these four components on the setpoint, fuzzy logic is used to determine the center of mass and, with that result, get the best setpoint value for the current moment.
How it is Done
Taking in consideration that the percent of energy saving for each chiller is different and depends on many factors such as chiller efficiency, operational healthy and environmental conditions, the GCOP Optimizer controller can be configured to operate in Evaluation Mode. In this mode, the optimization algorithms that resets the leaving chilled water temperature setpoint in real time are enabled only in even days and disabled in odd days. During the odd days, this setpoint is reset to a fixed value of 44 oF all day which is the current value if not optimization is applied. Every day the main chiller parameters are measured and saved in a Cloud data base.
The main goals of this evaluation mode are:
Get the real energy savings results
By comparing the average chiller percent of capacity (which is directly related with energy consumption) obtained the even days with the obtained for the odd days, the percent of energy savings for that particular chiller can be estimated more accurately.
Get a capacity reduction factor for the chiller plant
This factor is calculated using the difference between the average capacity for even and odd days, and the average variation of the leaving chilled water temperature setpoint during even days above the fixed setpoint value for odd days. In normal not evaluation GCOP mode, this factor makes possible to estimate the increase in the capacity of the chiller in real-time knowing the variation of the leaving chilled water temperature setpoint above 44 oF due to GCOP resetting algorithm, and so estimate the energy saving using the nominal tons and the tons/Kw of the chiller given by the chiller manufacturer
It is recommended to repeat the evaluation mode at least three times a year to take in consideration the seasonal changes that can impact in the real energy savings Also, it's possible to install power meters in each chiller and make all calculations using kW instead of chiller capacity.
Views of energy savings
The analytics that is running In the GCOP Web Server continuously calculates the estimated savings of energy showing the results in different graphics.
Savings trends chart
This chart describes for every chiller how the resetting of the leaving chilled water temperature (LCHWT) setpoint impacts in the current cooling capacity by showing what value would have the cooling chiller capacity if the minimal fixed set-point were used instead.
In the chart, the gray bar shows the changes of the LCHWT set-point above the minimum fixed set-point value (Delta SP). In the example figure shown, the LCHWT set-point has moved up to 4.3 oF above the minimum fixed set-point value. The blue line represent the actual chiller cooling capacity with the LCHWT set-point being reset by the GCOP controller and the red line represent the estimated chiller cooling capacity if the minimum fixed LCHWT set-point were used instead of the resetting algorithm. This estimated capacity is calculated by the GCOP controller using the estimated capacity reduction factor obtained during the Evaluation Mode. Using the nominal tons and the kW/ton of the chiller supplied by the manufacturer, the energy saved expressed in kW-h is also estimated in real time.
Based in how the GCOP controller calculates the savings when resetting the LCHWT set-point using the estimated capacity reduction factor, several saving energy reports are elaborated including last 30 day, monthly and year report. In those reports we can find many details that support the savings calculations such as capacity reduction factor used, running hours of each chiller, nominal tons, kw/tons, energy cost, average value of chiller capacity and average values of the variations in the LCHWT set-point above a fixed minimum value
Integration hardware support
Integration into BACnet field and remote control
First, the GCOP allows the integration of any BACnet MS/TP devices, i.e., the Wattnode Power Meters that can be used to verify the energy savings. Secondly additional BACnet device controllers can be installed in different zones to sense temperature and humidity that can be added to the GCOP optimization control logic. The new controllers and the GCOP can be routed into the existing BACnet architecture of the building using a BBMD, that allows BACnet messages to cross subnets which are interconnected with IP routers. Finally, it is possible to remotely access the GCOP controller and the additional controller’s program from the convenience of the systems integrator's home or office for maintenance and upgrade purposes.
This integration is possible thanks to the support of Contemporary Controls System, Inc. products.
The main Contemporary Controls products that can be used if required in the GCOP System integration support are:
BAScontrol22 and BAScontrol20 controllers
BAScontrol family of products provide all the features necessary for a truly open controller. If required, this controller is used in the GCOP system to monitor zone temperature and humidity, and use these values in the LCHWT setpoint reset optimization algorithms.
BAScontrol controller family is programmed using Sedona, an open source drags and drop component based programming language.
BASrouter model BASRT-B. BACnet Multi-Network Router
The BASrouter is used to route messages between BACnet/IP, BACnet Ethernet and BACnet MS/TP networks. If optional power meters are needed to verify the energy savings, the Wattnode Power Meters, with BACnet MS/TP protocol, are integrated to the GCOP using the BASRouter.
The BASrouter also supports 5 BBMD entries that allows the GCOP, if required, to integrate into the subnets of the existing BACnet topology in the building.
RemoteVPN. Simplified Secure Remote Communication
The RemoteVPN is a service offered by Contemporary Controls that allows systems integrators remote access to systems from the convenience of the systems integrator's home or office. This service is especially useful to make maintenance and upgrades in the Sedona program of each BAScontrol and provides a way to use a remote BMS for supervision and control.
Installation of the Bacnet IP network
Depending on the already existing Bacnet communication interfaces in campus, we install all the necessary communication interfaces, Gateways, and switches to make the Bacnet IP network up and running.
Installation of the GCOP Controller
All the required chiller parameters are mapped into the GCOP Optimizer Controller. The GCOP is also configured for optimum results for the characteristic of the target chillers
GCOP Cloud Analytics
A user account is created in the GCOP Web Server to monitor and have some control of the chiller plant anywhere you are. Historical trending graphics, evaluation and energy saving reports, and much more information about the chiller plant is displayed in dashboards.
Bacnet IP server for Integration
The GCOP Controller 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 GCOP controller and send back commands to the controller.
Continuous update of the GCOP Controller
Whenever a new software version is ready, the user can download it from the GCOP Web Server and install in the GCOP Controller.
Consulting and technical support
We prepare the maintenance operators in campus to operate the GCOP controller by them self, and we also give support and recommendations to get the best energy savings results.