Energy Master Planning for HVAC Systems in New and Existing Buildings

by Grahame E. Maisey, P.E. and Beverly Milestone, LEED AP
Building Services Consultants, Inc.

Last updated: 03-14-2007

Introduction

HVAC and energy systems play a large role in building energy efficiency and occupant comfort and productivity. Within high-performance buildings, these systems must perform much better than typical systems in every aspect: construction costs, energy, maintenance, and comfort. High-performance HVAC systems should have performance goals for net zero energy consumption—or better—and must be designed to require the minimum of materials for life-cycle installation, modifications, and alterations.

Sustainable, high-performance buildings generally require more planning and design effort than conventional buildings. Energy Master Plans (EMPs) provide the necessary steps to plan for HVAC and energy systems within a "whole building" context to achieve high-performance buildings. EMPs are "whole building" life-cycle plans, generally spanning from 40 to 100 years, instead of typical life-cycle performance programs that span the life cycle of the system only—usually 30 to 50 years.

A majority of funds spent on buildings during their entire life cycle is on the occupants' wages (see WBDG Productive Branch for more information). As such, it could be said that comfort and productivity are THE key indicators of high performance. Accordingly, EMPs stress the importance of systems maintenance throughout the building life cycle so that occupant comfort as well as energy performance are optimized and sustained. Maintenance requirements, therefore, also become a critical aspect of the design.

Description

A. EMP Goals and Objectives

Typical goals and objectives for a HVAC system could be: beat ASHRAE 90.1 by 30%, meet ASHRAE comfort criteria, and minimize installation cost.

EMP Goals and Objectives are very different: net zero energy use; optimum occupancy comfort for maximum occupancy performance throughout the building life cycle; minimum material use for the building life cycle; optimum maintenance throughout the building life cycle.

Note that the EMP refers to the building life cycle, not the HVAC system life cycle, so the planning is for the whole life of the building from initiation to deconstruction. The Goals and Objectives must all be met immediately, except the energy use. The energy use must be planned to be able to go to net zero in the future, but current economics might prevent immediate implementation of some renewable energy (e.g., solar photovoltaic and wind systems).

B. A Framework for Sustainability

There are different methods and systems available that present sustainability pathways for various situations. One such is The Natural Step (TNS) process, which has gained international acceptance. TNS begins by considering 4 conditions for sustainability and develops goals and objectives from these conditions and moves from there. The other principal method in the framework is back-casting, which takes the ultimate goals and objectives and then works back from them to the current planning situation. Essentially, what back-casting does is prevent the planning process from going down blind alleys, it maintains a focus toward true sustainability. The figures below summarize TNS concepts and how TNS is applied to Energy Master Planning.

C. Strategies for Sustainable, High-Performance HVAC Systems within EMPs

Comfort and Productivity

Optimizing comfort for the building life cycle is the most challenging strategy. Thermal comfort conditions include radiant and ambient temperature control, both of which must be controlled. Humidity and ventilation must be controlled year-round. Ventilation must also be controlled and used to prevent the spread of viruses and disease.

Thermal Control

Human beings are more sensitive to the Mean Radiant Temperature than Ambient Temperature. As such, radiant temperature control is essential for excellent thermal control. Fortunately, controlling the radiant temperature leads to strategies for saving energy and maintenance. In some cases—especially new construction—it is possible to use large areas for radiant cooling/heating to move the radiant system temperature closer to the room temperature, allowing an ambient temperature strategy to be initiated (using low temperature warming and high temperature cooling, 10°F to 30°F different to room temperature). See also WBDG High-Performance HVAC.

Humidity Control

Desiccant dehumidification control will be necessary in geographic areas where there is high humidity. Liquid desiccant systems are most promising and it appears there will be systems available in the near future that will be applicable to institutional, commercial, and residential as well as industrial situations. In geographic areas that have cold weather, desiccant humidification control will also be necessary.

Ventilation Control

As will be explained in the next paragraph, minimizing the amount of air distributed throughout the building is essential. One of the most efficient ventilation strategies is displacement ventilation. Most situations only require 0.15cfm/ft² ventilation air most of the time. Outside conditions of high humidity, low temperatures causing low humidity, or large increases in occupancy can cause a tripling of the air requirement, up to 0.35cfm/ft². Ideally, two or three ventilation levels would optimize air distribution and ventilation supply, with the system(s) supplying 0.12cfm/ft², 0.24cfm/ft² or 0.36cfm/ft².

Controlling viruses that can spread by airborne transports and cause diseases such as the common cold requires controlling the flow of air throughout the building. Controlling the flow of air through the envelope is the first priority, which is done by good envelope systems (i.e., wall, window, and roof). Controlling the flow of air between floors is the next priority, and this can be done through sealing floors and minimizing thermally caused flow by balancing the airflow and carefully controlling the temperature differences between floors. High-rise buildings need special efforts to control air flow caused by thermal currents, hot air rising, and cold air falling. See also WBDG Air Barrier Systems in Buildings.

Controlling the spread of viruses will also be improved by supplying only cleaned and treated outside air and eliminating return air that could be contaminated with and by anything inside the building. When supplying minimum ventilation air, it is easy to supply 100% outside air, but when 1cfm/ft² or more (which is the case in most HVAC air systems) is distributed throughout the building, it is usual to recirculate up to 90% of the air. In some cases, it is better to supply 100% outside air and use energy recovery systems than risk the health of the occupants. For example, schools, hospitals, and offices are notorious for spreading colds and flu, and a major culprit for this is the HVAC system. See also WBDG Air Decontamination.

Energy Use

EMPs focus on moving the energy use to net zero for the building life cycle. To achieve this objective requires planning and long-term strategies. Planning for the system to be net zero energy use for the current building layout is not the only challenge; the systems will also need to be flexible, adaptable, and expandable to cater to foreseeable future modifications and alterations while sustaining efficiency. Often, a modular approach to building floorplate design will allow different layouts and uses to operate with the same efficiency and minimum modifications.

Examining the energy use of the HVAC system components and the longevity of the components is necessary. In a typical HVAC system, over 50% of the total energy use and over 50% of the total system cost is from the distribution systems, pumps and fans, ductwork and piping. Moreover, 75% of typical remodeling costs are for the distribution systems. Optimizing the distribution systems should be priority #1. Based on actual case studies by the authors of this Resource Page, an optimal, high-performance design has been shown to reduce the energy use by over 85% and reduce the materials use for the building life cycle.

Piping systems are 10 times more efficient for transporting thermal energy as compared to air distribution. Also, piping distribution requires only 10% of the space an air duct requires. Piping systems and radiant systems are complimentary, so it would seem logical to use radiant piping systems for heating and cooling. The reluctance to use radiant cooling panels in geographic areas east of the Mississippi is due to the high humidity levels potentially causing condensation. This is why an efficient and effective desiccant dehumidification system is so essential to sustainable, high-performance systems. Minimizing the piping material use for the building life cycle and minimizing the energy use requires proper system selection. The typical system for piping is a flow and return system. A durable facility will require a flexible, adaptable, and expandable system that can maintain performance at a minimum pumping energy use level, which is about 90% less than conventional systems.

An equal pressure or reverse return system is one solution for this design problem. Low load and high load pumps reduce the energy use by over 85%, and the system is also flexible, adaptable, expandable, and maintainable. Flow and return piping systems remain the dominant choice by designers, chiefly because connecting the dots is easier than planning out a distribution network. While common practice is to use constant pressure, variable speed pumping to two-way valving from a variable frequency drive matched to a high efficiency pump, the authors of this Resource Page have found that this system requires a maintenance intensive pump that consumes 5 times more energy than a small pump on the equal pressure system, and is not as expandable, flexible, or adaptable.

Within the EMP, eliminating fossil fueled systems is a major objective for a facility designed for environmental sustainability. In areas east of the Mississippi, refrigeration is needed more for humidity control than for cooling, and a desiccant humidity control system will accomplish humidity control without refrigeration, requiring only 180°F hot water for dehumidification and 62°F cooling water for the ventilation air and the radiant cooling. Examples of sustainable technologies—those that do not depend on fossil fuels—to provide the 180°F hot water for dehumidification and the 62°F cooling water include solar hot water heating and ground source systems, respectively. For heating requirements, ground source combined with solar hot water can also be adequate in many situations and geographic areas. Note that while these systems are not applicable in all situations, the project team should consider options to achieving net zero energy use. Also, cooling and heating do not have to be dependent on the consumption of fossil fuels.

Maintenance Optimization

Sustainable maintenance, which begins with minimizing maintenance requirements, is key to a sustainable building, particularly for its energy systems. At present, there are many facilities that have a "deferred maintenance program." Yet, based on the experiences of the authors of this Resource Page, maintenance deferment has been shown to cost the facility substantially more money in the long-term.

Sustainable maintenance requires substantial planning and effort early in the design process, and minimizing the maintenance requirement is one of the most challenging strategies to achieve. There are three conditions that must be fulfilled to achieve sustainable maintenance:

• All moving parts must be in plant rooms;
• If the systems, equipment and components are not easy to maintain, they will not be; and
• Typical maintenance programs will reduce maintenance effort through the building life cycle even though the maintenance requirements may rise as the systems age.

Materials Minimization

Whole building life-cycle material use assessment requires planning derived from experience and informed maintenance and use anticipation. The concept of "long life; loose fit" fails to meet expectations when it does not include "high performance" in its mantra, resulting in mediocre building performance from day one. However, "long life; loose fit; high performance" is a reasonable assessment of what we want to achieve with EMPs. Current building layout and use may change substantially, so a reasonable assessment of probable future modifications and alterations will allow the different scenarios to be taken account and the systems designed with these in mind. The systems must be flexible, adaptable, and expandable, but the magnitude and extent are the million dollar questions.

The distribution systems are key to success. The authors of this Resource Page recommend the piping system to be the equal pressure type with adequate capacity and modularity for the future. Also, radiant heating and cooling systems should be assessed and considered for their life-cycle performance and cost-effectiveness because they could last for 80 to 100 years with the new plastic technologies available. Lastly, ductwork distribution should be assessed for future modifications and designed to be flexible and adaptable. Systems similar to the piping systems, which are different to conventional systems, should be considered as well.

D. Conclusions

Energy Master Planning represents the future model for energy systems in sustainable buildings and facilities. The investment of effort and expertise necessary to develop EMPs is rewarded many times over by the improvements in facility performance, enhanced productivity, and operational cost savings.

Only by planning for sustainability can it really start to happen. Unfortunately, rule-of-thumb "Green Guidelines" and "Best Practices" are insufficient for EMPs because they may lead to incorrect HVAC system and equipment selection and sizing. EMPs require careful planning, application of sound engineering principles, and life-cycle maintenance considerations.

For example, fan-assisted variable air volume HVAC systems are popular and are being installed in a wide variety of applications throughout the country. The system is convenient and easy to design. Yet, based on the experiences of the authors of this Resource Page, it is also expensive to install and modify, very expensive to maintain, and has yet to provide long-term energy savings. The conceptual problems with this system from a life cycle, EMP viewpoint include intensive maintenance requirements, lack of radiant control and extensive air distribution, including recirculating air. By applying sound engineering principles, it can be found that this system would not be selected in many situations. As such, it is recommended that the design team thoroughly analyze the appropriateness of popular systems and do not readily accept packaged solutions. See also WBDG Functional/Operational Branch.

Application

Energy Master Plans (EMPs) provide the necessary steps to plan for HVAC and energy systems within a "whole building" context to achieve high-performance buildings. EMPs can be developed for all building types and are especially useful for high occupancy buildings and/or complicated ones such as educational facilities, office buildings, health facilities, and research facilities. Ideally, EMPs would be developed when the building is being first designed. However, EMPs can also be developed for existing buildings in anticipation of future expansion and modifications.

Relevant Codes and Standards

• Energy Policy Act of 2005 (PDF 1.9 MB, 550 pgs)
• ASHRAE Hand Books
• ASHRAE Energy-Efficient Design in New Buildings Series 90,
• ASHRAE Energy Conservation in Existing Buildings, Standard 100-1995
• CIBSE Guide F, Energy efficiency in buildings
• CIBSE Research Report 4, Engineering design calculations and margins—Free for members to download from Members Area

Additional Resources

WBDG

Building Types

Applicable and relevant to all building types

Design Objectives

Cost-Effective, Functional / Operational, Historic Preservation—Update Building Systems Appropriately, Productive—Assure Reliable Systems and Spaces, Productive—Promote Health and Well-Being, Productive—Provide Comfortable Environments, Sustainable—Optimize Energy Use, Sustainable—Enhance Indoor Environmental Quality, Sustainable—Optimize Operational and Maintenance Practice

Products and Systems

Section 23 05 93: Testing, Adjusting, and Balancing for HVAC, Building Envelope Design Guide
Federal Green Construction Guide for Specifiers:

• 23 70 00 (15700) Central HVAC Equipment
• 23 30 00 (15700) HVAC Air Distribution

Project Management

Building Commissioning, Project Delivery Teams, Project Planning and Development, Project Delivery and Controls

Organizations/Associations

• ASHRAE—A leading organization in the development of standardized commissioning guidelines.
• U.S. Green Building Council

Publications

• The Architecture of Building Services by Gordon Nelson. B.T. Batsford, 1995.
• Design With Climate by Victor Olgyay. Princeton University Press, 1963.
• Energy and Environment in Architecture. Baker and Steemers.
• The Energy Design Handbook by Ed. Donald Watson. Washington, DC: AIA Press, 1993.
• Fundamentals of Building Energy Dynamics by Ed. Bruce D. Hunn. The MIT Press, 1996.
• The Idea of Building by Steven Groak, E & FN Spon, 1992.
• Inside Out by Brown, Haglund, Loveland. New York, NY: John Wiley & Sons, Inc., 1982.
• Passive Low Energy Cooling of Buildings by B. Givoni. New York, NY: John Wiley & Sons, Inc., 1994.
• Passive Solar Commercial and Institutional Buildings by Ed. S.R. Hastings. New York, NY: John Wiley & Sons, Inc., 1994.
• Practical Thermal Design in Buildings by Peter Burberry. Batsford Press, 1983.
• Thermal Control of Buildings by D.J. Fisk. Applied Science Publishers, 1981.