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Optimization Strategies

Packaged Central Plants
 

Adaptive Control: Continuous, Real-Time Energy Optimization to Save Energy and Money!

Real energy optimization requires a control strategy to deal with the continually changing real world conditions in your HVAC system.  tekWorx meets this challenge head on by applying its proven adaptive control techniques your system - NO canned BAS programs or equipment vendor sequences that just deal with the chiller.  A closer look at tekWorx' distribution pump control illustrates how adaptive control saves money.

Using design parameters (flow, head, friction loss), tekWorx generates a Pump kW Consumption Analysis for each specific system, similar to the example shown (left). The curves illustrate the point above which the kW required to operate one pump is actually more than that required for two pumps to deliver the same flow.

The corresponding kW value is loaded in the control program and used to sequence ON / OFF the lag pump in the initial operation. The adaptive control algorithm then analyzes the actual system behavior during each sequence operation, and makes an on-line adjustment to the sequence point for the following operation. The result is that the optimize setpoint is continuously used, thus dramatically reducing pump energy consumption.

The Pump kW Consumption Analysis tool, in conjunction with the adaptive control techniques provide one other benefit that saves both cost and operating expense. Design engineers can accurately select the minimum size distribution pumps to safely get the job done.
 

One significant yet hidden benefit: the adaptive algorithm assures that pumps always operate in the eye of their efficiency curve, thereby reducing radial stress. By eliminating this major cause of seal wear, maintenance costs are greatly reduced.

Variable Primary Pumping

Advances in chiller design and digital control technology in the past few years have caused a fundamental shift toward Variable Primary (VP) design for distribution pumping, and there are now thousands of successful VP installations. VP's proven reliability, energy savings and ability ot maximize plant capacity have rendered the venerable Primary/ Secondary method (P/S) obsolete. A comparison of the two designs readily shows why.

P/S Basics P/S system (shown at the left) consists of two pumping loops that share a common pipe. The primary loop (also known as the production loop) uses constant speed pumps to circulate a fixed volume of water through the chillers. The secondary loop (also referred to as the distribution loop.) uses variable speed pumps to deliver the required volume of water to satisfy the load. The volume of water is regulated by the speed of the secondary pumps which is controlled to maintain the remote P setpoint. This arrangement allows a constant volume of water to be circulated through the chillers, while the flow through the common pipe varies in relation to the flow required to satisfy the load. Thus, at a light load, the low pump secondary speed means that a high volume of water is bypassed back to the chiller; very little water bypassed at a high load because the high secondary pump speed draws most if not all of the water off the primary loop and sends it to the load. While this system "works" to produce cooling, the system T varies with the amount of water being bypassed, and the energy energy performance and available capacity varies with it.

VP Basics  In contrast, the VP design (shown at the right) has only one loop, so it uses only one set of variable speed pumps to circulate water through both the chillers and the load. The pump speed is still regulated to maintain the remote P setpoint (just like the P/S system.)  The VP system has a control valve in the bypass line that opens during light load conditions to insure minimum evaporator flow. When this valve is closed (which is most of the time) there is no flow through the common pipe, and thus there is no negative impact on DT.

Summary of Variable Primary Benefits

  • Superior energy performance - less pump energy, no negative impact on T

  • Full Use of Capacity: efficient chiller loading.

  • Low first cost: fewer pumps, less piping, simpler electrical installation

  • Small physical space more productive usable/rentable space

  • Flexibility / Backup Pumps and chillers are headered, so that any pump can run with any chiller

  • Reliability and Maintenance less equipment mess less equipment failure.

 

 

Delta-T Compensation for Chiller Staging

tekWorx adaptive control combats the virtually inevitable low T condition and it's adverse affect on chiller energy usage. Our exclusive T compensation algorithms dynamically re-calculate chiller staging points to reduce unnecessary chiller operation.  This technique also maintains higher kW per ton by keeping chillers more fully loaded. A common example of this terribly inefficient condition occurs when two chillers each provided 50% of the cooling at a lower kW per ton than would otherwise be present if a single chiller provided 100%.

Condenser Water Optimization

This adaptive control technique yields the optimum condenser water temperature for the current cooling load and operating conditions. The algorithm continuously balances the energy associated with a higher cooling tower fan speed against the corresponding increase in chiller efficiency afforded by a lower condenser water temperature. Thus, the chiller continuously operates at the optimum condenser water temperature, which directly translates into big energy savings.

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