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©2017 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 59, no. 12, December 2017

By Ross Montgomery, P.E., BEAP, BEMP, CPMP, HBDP, Fellow ASHRAE

About the Author
Ross D. Montgomery, P.E., is president and owner of Quality Systems and Technology Inc., a commissioning provider company based out of Parrish, Fla.

Chilled water thermal energy storage systems (TES) have been used successfully in district cooling systems for decades. According to the 2016 ASHRAE Handbook—HVAC Systems and Equipment,1 thermal storage systems “remove heat from or add heat to a storage medium for use at another time.” These TES systems can come in the form of ice or cold-water storage. This article focuses on the commissioning of systems and the sequence of operations for individual school project chiller plants and cold water thermal energy storage systems using a large storage tank (Photo 1), performed on a large group of individual educational facilities over the course of 2012 – 17. The sequences and commissioning tasks have been refined over time to improve the final deliverables and performance to the facilities.

The capacity design of the TES system used is tailored to the individual needs of the facility itself. In general, an example design for one school would be an air-cooled chiller plant consisting of two 400 ton (1407 kW) chillers operating at 42°F (5.6°C) to 56°F (13.3°C) supply/return temperatures, chiller and charge primary flows at 1,370 gpm (86 L/s), discharge primary flows at 1,500 gpm (95 L/s) and secondary flows up to 3,000 gpm (189 L/s). The thermal storage tank capacity is 4,800 ton-hours (16 880 kWh) and holds 600,000 gallons (2.3 million L) of treated water. In some projects, water-cooled chillers with cooling towers were also used.

Building commissioning in its early days was performed by its consulting engineer designer and their staff as a part of continuing design services. Starting in the early 1980s, when ASHRAE started to develop its Guideline 0 and Guideline 1 on commissioning, and later its ANSI/ASHRAE/IES Standard 202, Commissioning Process for Buildings and Systems, buildings can now be professionally commissioned by third-party independent commissioning providers.

Benefits of cold-water storage include:

  • Shifting loads and kW demand from peak- to non-peak times (in both summer and winter) allow for participating utility incentive payments and discounts and current utility rebates, relative to thermal water storage;
  • Discounts and rebates from participating utility(s) reduce costs of new equipment purchases;
  • If a time-of-use (TOU) rate is available from the utility company, energy cost savings can be obtained by operating the chiller equipment in a central plant more during the off-peak periods, and reducing the energy consumption during peak periods;
  • Increased energy efficiency of chiller equipment by operating them at night in cooler ambient conditions (cooler nighttime condensing water temperatures);
  • Reduced sizes of required HVAC and electric equipment/devices in some cases;
  • Increased operating flexibility and scheduling;
  • Backup capabilities and extra capacity to the facility in case of equipment malfunction or failure;
  • Assistance to integrate renewables into systems; and
  • Dual-purpose fire protection water supply.

Construction Commissioning Process

Commissioning can begin at predesign, design, or during construction. This article will focus on the efforts taken during construction commissioning. At the beginning of any construction commissioning project, it is vital to make sure the owner’s project requirements (OPR), in the case of new construction, or current facility requirements (CFR), in the case of existing buildings, are monitored and followed while performing the standardized commissioning tasks for new construction, as outlined and discussed in detail in ANSI/ASHRAE/IES Standard 202-2013.2 Those steps can be summarized as:

  • Initiating the commissioning process;
  • Writing the commissioning plan;
  • Reviewing the design and construction documents;
  • Creating and working with the commissioning team;
  • Performing commissioning submittal review;
  • Performing construction observation and testing;
  • Performing the functional performance testing;
  • Maintaining the issues documentation and resolution logs;
  • Observing the training process including using the systems manual and record documents as training materials;
  • Monitoring post occupancy operations; and
  • Writing the final commissioning report.

 

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