Central Plant / District Energy Engineering

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Contemporary central plant design seeks to achieve new levels of energy efficiency for a single building or campus by linking together heating, cooling and power generation in advantageous ways. For example, the heat energy remaining in steam used to drive electric generation turbines can be used to heat or cool buildings.  District Energy systems scale up these efficiencies of integrated heating/cooling/power by applying them to groups of buildings or multi-block sections of a city. (For information about how District Energy St. Paul heats and cools 185 buildings in downtown St. Paul, MN, click here.) Goss Engineering is an adviser to District Energy St. Paul for the application of thermal energy storage technology and techniques.

In designing District Energy systems, engineers and architects seek to integrate all the available energy technologies and methods that are appropriate for a given climate zone, from electronically-controlled louvered windows on buildings to thermal energy storage(TES) and combined heat and power(CHP). (Click here to download a 60-page report from the International Energy Association about the contribution CHP makes in District Energy projects.)

Applying these technologies and disciplines, Goss Engineering acted as a consultant to the project mechanical engineer in developing the central plant component of the master plan for the new University of California Merced campus. Seven buildings on the new campus have earned LEED Gold awards. To read an environmental sustainability review of the library building shown below, click here .

Kolligian Library, University of California Merced   

As part of our Central Plant and District Energy design consulting practice, Goss Engineering is proud to be a participant in the  Combined Heat and Power (CHP) Partnership  of the U.S. Department of Environmental Protection, which promotes energy efficiency in the United States and around the world.

Goss Engineering is proud to be a participant in the Combined Heat and Power (CHP) Partnership of the U.S. Department of Environmental Protection.





(Includes both TES and CHP projects.)







Goss Engineering is an active participant in the evolution of Central Plant / District Energy Storage design practice in the United States. Goss Engineering staff members have authored/co-authored/edited the following articles and books in the field (partial listing).


Sustainable Thermal Storage Systems: Planning, Design and Operations

A practical guide on how to plan, design, and construct sustainable thermal storage systems.

    • Defines sustainable thermal storage
    • Discusses the types of facilities that can benefit from thermal storage
    • Outlines the various types of thermal storage systems available
    • Presents the key requirements in thermal storage planning
    • Includes thermal storage system sizing examples
    • Contains performance metrics
    • Explains how to conduct a feasibility study
    • Features case studies that demonstrate real-world applications

cover of thermal energy storage textbook Use of thermal storage—also called thermal energy storage (TES)—can result in: reduced on-peak electric demand; reduced energy costs; smaller required chiller capacity to meet peak cooling demand; lower capital costs; lower life cycle costs; improved operational flexibility; less air pollution. This book covers all of these aspects.


    • Overview
    • Applicability of Thermal Storage Systems
    • Types of Thermal Storage Systems
    • Sensible Thermal Storage Systems
    • Latent Thermal Storage Systems
    • Heat Storage Systems
    • Thermal Storage Sizing
    • Conducting a Feasibility Study
    • Thermal Storage System Design Applications
    • Control Strategies and Requirements
    • Thermal Storage Specifications and Construction Process
    • Commissioning
    • Operations and Optimization
    • Case Study: Chilled Water Storage at Linda University;
    • Case Study: Ice Storage System


Sustainable On-Site CHP Systems: Design, Construction and Operations

A 2009 engineering textbook book published by McGraw-Hill

######### Plan, design, construct, and operate a sustainable on-site CHP (combined heat and power) facility using the detailed information in this practical guide. Sustainable On-Site CHP Systems reveals how to substantially increase the energy efficiency in commercial, industrial, institutional, and residential buildings using waste heat and thermal energy from power generation equipment for cooling, heating, and humidity control. In-depth case studies illustrate real-world applications of CHP systems.


Commissioning Chilled Water TES Systems from Engineered Systems Magazine, 2004

By Lucas Hyman, P.E.


The goal of the commissioning process is to deliver a project that, at the end of construction, is fully functional and meets the owner’s needs. Some of the fundamental objectives of the commissioning process are to:

  • Clearly document the owner’s project requirements (OPR);
  • Provide documentation tools (basis of design, commissioning plan, design, and construction checklists);
  • Help with coordination between parties (owner, engineer, and contractor);
  • Accomplish ongoing verification that the engineering and construction achieve the OPR;
  • Verify that complete O&M manuals are provided to the owner;
  • Verify that maintenance personnel are properly trained; and
  • Accomplish functional performance tests that document proper operation prior to owner acceptance.

This article highlights the following:

  • Key OPR for a stratified CHW TES system;
  • Successful CHW TES design strategies (basis of design);
  • Caution flags (lessons learned);
  • Guidelines of ASHRAE Standard 150, “Method of Testing the Performance of Cool Storage Systems requirements;” and
  • Key CHW TES information to obtain during testing.

  full article in PDF format  


Overcoming Low Delta T

from ASHRAE Journal, February 2004   

By Lucas B. Hyman, P.E. and Don Little 

The University of California, Riverside (UCR) in Southern California is the fastest growing campus in the UC system. The campus has approximately 3 million ft2 (279 000 m2) of assignable facilities, including many science buildings with 100% outside ventilation air. Planning and modifying the campus’ chilled water system has occurred slowly, as resources were available. Unfortunately, those modifications have not always kept up with the campus’ rapid expansion.

Moreover, a lack of enforced chilled water system design standards resulted in many different building interfaces. The resulting problems with the chilled water system included unexpected low, and even negative, differential pressure (Delta P) near the end of chilled water distribution mains, and high chilled water system Delta P near the central plant. The unexpected low and negative Delta P resulted in low chilled water flow and thermal comfort complaints in buildings located at the affected ends of the distribution system. At the same time, high Delta Ps near the central plant forced open control valves, contributing to the central plant experiencing low chilled water temperature differential (Delta T). This resulted in loss of thermal energy storage (TES) capacity, increased pumping energy, and reduced available cooling capacity.

Specific causes of the chilled water problems included:

1. A mixture of constant-speed series tertiary pumps and tertiary pumps with bridge connections;

2. Secondary distribution piping constraints caused the secondary pumps to be inadequate to the task of keeping the distribution system positive;

3. Lack of variable speed drives (VSDs) on the series tertiary pumps;

4. Flow limitations through the TES system which could no longer carry the full peak load;

5. Coils selected for low delta-T (10°F to 12°F [5.5°C to 7°C]);

6. Some chilled water bypassing; and

7. Reverse or inoperable controls.

Thermal comfort complaints resulted primarily from a lack of chilled water flow to the buildings experience negative differential pressures. The chilled water systems for the affected buildings were not designed for negative differential pressures (i.e., the chilled water pumps did not have enough head for this condition). The design team developed a multifaceted approach to solve the problems.

Solutions included:

1. Modifying the existing chilled water distribution system to reduce system drops and system constraints;

2. Adding a central plant secondary chilled water distribution pump to increase pumping capacity;

3. Installing, at buildings near the central plant, modulating two-way pressure independent control valves (PICVs) to improve controllability at high Delta Ps and to help prevent chilled water bypassing via forced open control valves;

4. Converting from a full storage TES operational strategy to a partial storage strategy; and

5. Stopping short circuits (bypass of chilled water supply to return), correcting reverse logic on some control valves, and addressing other control deficiencies.

VFDs were not added to tertiary pumps because the campus limited the scope of any actual building chilled water system work. After the modifications were completed, the UCR chilled water distribution system achieved a positive Delta P at the end of the piping mains, achieved cooling thermal comfort in previous problem buildings, and attained a 20°F (11°C) Delta T in the chilled water and TES system.

full article pdf  



from industry, university and government sources

Catalog of CHP Technologies from the U.S. Environmental Protection Agency

The  Catalog of CHP Technologies (PDF)  (all chapters, 139 pp, 1.5 MB) provides an overview of how combined heat and power (CHP) systems work and the key concepts of efficiency and power-to-heat ratios. It also provides information about the cost and performance characteristics of five commercially available CHP prime movers.

Download chapters from the Catalog of CHP Technologies:

Central Plant Design Options  from the BetterBricks web site of NEEA (The Northwest Energy Efficiency Alliance).

A central plant can be the centerpiece of a commercial facility’s energy efficiency and the resulting benefits – lower operating costs, greater comfort, health and productivity for occupants, better tenant retention, higher property values, and cleaner air due to reduced power plant emissions.

Central Plant Measures

    • High-efficiency water-cooled chillers
    • Variable-speed drives on chillers
    • Chiller staging
    • Variable-speed drives on secondary chilled water pumps
    • Variable-capacity chiller controls
    • Variable-speed drives on cooling tower motors
    • Oversized cooling tower


The High Performance Buildings Database
of the U.S. Department of Energy


International District Energy Association (IDEA) 

UK Community Energy: Planning, Development and Delivery Guide (PDF)

IDEA fosters the success of its members as leaders in providing reliable, economical, efficient and environmentally sound district energy services. We promote energy efficiency and environmental quality through the advancement of district heating, district cooling and cogeneration (also known as combined heat and power or CHP) and we actively lobby to secure favorable policies, legislation and regulations for district energy.


Catalysts for Change — Article in December, 2011, issue of Canadian Consulting Engineer

[Excerpt] University and college campuses provide ideal opportunities for reducing carbon emissions from our built environment [by adopting District Energy strategies].

Across the University of Toronto’s downtown St. George campus are 120 large buildings — over 12 million square feet of space — all consuming energy. The buildings range from heavy masonry Victorian structures like the venerable Mining Building on College Street, to sleek glass boxes such as the Pharmacy Building at the corner of University Avenue.

To walk from one side of the campus to the other takes about 20 minutes. The site is threaded with busy streets and narrow laneways, some of which are owned by the university. There are shady paths, wide open sports fields, and secluded courtyards. Like many of Canada’s universities, the campus represents a quiet oasis in the heart of the teeming city.

But Canadian university and college campuses are becoming much more. They provide an almost ideal incubator for developing ways of making our buildings and cities more energy efficient. The campus is like a mini-town, with many different types of buildings and facilities — but all under one owner. Generally there is one department in charge of buildings and facilities and those people work under a ruling administration that is relatively free of political and other constraints. So it can be easier to reach decisions about building in a sustainable way in the campus environment than in the messy “real” world outside.   more


Energy Storage: A Critical Path to Sustainability
Mark M. MacCracken, PE, LEED AP, President, CALMAC [manufacturer of thermal storage equipment]

[Excerpt]   To understand the importance of storage, it is imperative that one understands the electric power grid. If you have ever lived in a warm environment, you have probably experienced a brown-out. Brown-outs typically happen in the heat of day, when the temperatures are high and buildings across the area are turning up the air-conditioning and creating an enormous need for energy. Because of this, in the middle of any day, the demand on the power grid is the highest. In addition to the air-conditioning running at full power, more lights are on and multiple appliances are in use. Because of the strain on the grid, the costs for electricity are highest during those “on-peak” hours and the generation is often the dirtiest since all the old plants are turned on to help meet the demand. On the flip side—at night—when the majority of people are sleeping, there is a very low demand on the grid, and sometimes, even over-capacity. This is called “off-peak.”

Storage is the Answer:  In its present configuration, our electric grid has almost no “storage” capability so that electricity must be produced exactly when it is needed. This is possible when your source of energy is fossil fuel (stored energy) but is very difficult and expensive when it is renewable energy (wind or solar). Adding energy storage to the grid will be critical in our quest to lower societies’ carbon emissions.

Acheiving Plant Optimization    By Dave Klee of Johnson Controls.  An article in the Daily Energy Report.

Buildings – big and small, old and new – are collectively the largest consumers of energy worldwide. Within each individual building, the heating, ventilation and air-conditioning (HVAC) systems consume the most energy. An even closer look at a building’s various HVAC systems will reveal that it’s the building’s central chilled water plant that is the biggest energy glutton.


Resources from the Canadian District Energy Association

The Canadian District Energy Association (CDEA)/Association Canadienne des Réseaux Thermiques (ACRT)   is an industry association representing member utilities, government agencies, building owners, consulting engineers, suppliers, developers, bankers, and investors who share a common interest in promoting the growth of district energy in Canada.