HVAC System Dynamic Integration

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

Last updated: 08-10-2010

Introduction

"The greatest opportunities for saving costs over the life of a building occur at the beginning of the design process." AIA Energy Design Handbook

An Amory Lovins national building survey in 1992 concluded: "A lack of integration in the design process has made buildings costlier to build, costlier to cool, and less comfortable than they should be."

This situation remains true today, especially for HVAC systems that are being imposed on buildings rather than integrated into them. Oftentimes, HVAC systems are selected and sized according to minimum code requirements and maximum design loads. These poorly selected, vastly oversized systems are costing building owners billions of dollars each year in energy costs and low occupant performance and effectiveness.

Architects use the holistic and dynamic nature of buildings as the foundation for passive energy designs. Using the dynamic nature of building energy flows and integrating the HVAC system into these flows creates a dynamically integrated HVAC system design as part of a "Whole Building" Design. For more information on "whole building" design, see WBDG Whole Building Approach.

Dynamically integrating HVAC systems into the building architecture picks up where architects leave off—by continuing to utilize the dynamic nature of building science to create true HVAC system integration and sustainability. Dynamic integration helps to ensure that HVAC systems are selected and sized correctly using appropriate criteria. These HVAC systems will produce environmental comfort that promotes optimum occupant performance and satisfaction while costing the least to operate and maintain.

Sustainable building design must incorporate both passive energy design strategies by the architect and dynamic integration design strategies by the HVAC designer.

Description

Architects design buildings to mesh with the rhythms of nature: the hot radiance of the daytime sun, the cold black radiance of a clear night, and the diurnal temperature swings all profoundly affect building thermal systems. Dynamic integration develops HVAC systems to fit in with the building environment the architect initiates.

Dynamic integration is a two-step process: first static integration, then dynamic integration. Static integration "right sizes" the equipment by closely examining the numbers used in the design criteria and double-checking the calculations for cumulative errors, This may result in reduction of equipment sizes by an average of 30%. See also WBDG High-Performance HVAC.

A. How to Apply Dynamic Integration

Dynamic integration is an iterative process that tests the HVAC system selection criteria by examining the system performance through various operating strategies and performance requirements. Thus, dynamic integration correctly selects and sizes HVAC systems making them more efficient to operate and provide optimum indoor comfort to maximize productivity and performance. See also WBDG High-Performance HVAC.

Applying various operating strategies allows different system characteristics to be isolated and incorporated, resulting in the development of new system selection criteria to answer the strategic demands and requirements of the building operation. Modern digital, computerized controls are the biggest innovation in HVAC equipment, allowing accurate and remote control of building systems and allowing strategies to be developed and applied modularly or globally to the systems. Applying different energy reduction strategies allows different system selections to be analyzed.

Strategies include:

• Use the thermal mass of the building to minimize cooling and heating loads. See also WBDG Passive Solar Heating.
• Cool buildings overnight to reduce the peak cooling load
• Pre-ventilate the building to minimize ventilation loads during peak hours
• Utilize ground coupling to greatly reduce cooling and heating loads
• Minimize the dehumidification load
• Utilize desiccant humidity control systems to minimize refrigeration loads
• Reduce/Remove the refrigeration load
• Reduce/Remove the boiler load
• Optimize thermal comfort by combining radiant and air temperature control
• Optimize thermal comfort by providing optimum humidity control
• Optimize occupant comfort by providing the best ventilation
• Optimize occupant comfort by providing the cleanest air.

For more information on high performance HVAC strategies and equipment, see See WBDG High-Performance HVAC.

Using these operating strategies, system selection can be optimized. Many times, the size of the system can be reduced 30% on average, creating a HVAC system half the size of a conventionally designed system. Electrical energy reduction is a priority, so minimizing distribution energy and eliminating refrigeration equipment should be the first focus of the energy strategies. Buildings should eliminate refrigeration if they have a ground source temperature available of 65°F or less, which includes most areas north of the 36° parallel, north latitude (Virginia and north on the east coast and San Francisco and north on the west coast).

HVAC system selection may depart from an all-air system. Such a system uses twice the energy for distribution than a piped system and cannot take full advantage of building mass nor provide adequate radiant thermal control.

Long-term operating efficiency is examined closely. Cleaning and lubrication of all moving parts remains 90% of the maintenance duties of any HVAC system, therefore this is examined in the system design criteria.

Physical integration, both static and dynamic integration, integrates the energy systems into the building fabric, i.e. walls, floors, columns, etc. Pipes, ductwork, photovoltaics, etc., can be integrated into the building to create a more energy efficient, healthier indoor environment. This incorporation can take place in a new building, or in the rehab or major modification of an existing building.

The case study below illustrates the effects of Static and Dynamic Integration on HVAC systems for a 200,000FT² office block.

Application

Whole Building dynamic integration can be applied to any new building design or major remodeling project. It is for the architect and owner who want a truly super-efficient HVAC system that is flexible and adaptable to change, and who are seeking personnel productivity increases. This technique works exceptionally well with sustainable design concepts.

Case Study

EXAMPLE: A 200,000ft² office block in Philadelphia

Current Design:

A standard HVAC system is a Variable Air Volume system with heating zone coils for winter, a 550 ton electric centrifugal chiller, and two 5,000,000 BTU/hr gas fired water tube boilers. The VAV system distributes 1cfm/ft² of occupied space, 160,000cfm, the annual fan volume averages 80% of the design volume, 130,000cfm.

Whole Building dynamic integration design:

Start the design process by testing client requests and the preliminary client brief. Most clients seek to minimize the HVAC operating costs and maximize the occupant performance while keeping the installation costs minimal. High occupant performance requires good ventilation, low noise, low air movement, individual temperature control, a mixture of 33% ambient air and 67% radiant temperature control to give the most comfortable occupant temperature control, humidity control to a maximum of 45%RH in the summer and a minimum of 35%RH in the winter. Minimum operating costs require maximum long-term energy and maintenance efficiency.

Typical HVAC designs immediately convert the radiant heat control system of the passive building architecture into an air temperature control system. Dynamic integration utilizes the radiant control that the architecture generates from the large thermal energy embedded in the mass of the building.

Dynamic integration uses the building and the environment to work with the HVAC system. The building has a large mass in the floors, columns, and external walls, that have large thermal absorption capacities. Philadelphia is hot and humid in the summer, cold and dry in the winter, but the average temperature is 55°F, this can be used to great advantage.

Typical HVAC air distribution systems not only use 50% of the total energy consumption, but it is electrical energy, so an efficient HVAC system must reduce this by 75%. Water is three times more efficient at moving heating and cooling energy than air. Using a piped distribution system reduces the electrical use by 65%. Reducing the amount of air moved throughout the building by 70% reduces fan power by 90%.

Year round humidity control is a priority; it can have a larger effect on health than temperature. Maintaining humidity in the winter and reducing humidity in the summer allows temperatures within the building to be adjusted down in the winter and up in the summer while maintaining optimum comfort levels. A liquid desiccant humidity control system uses heat in the summer to dehumidify and adds humidity in the winter, as well as energy recovery from the ventilation exhaust system. A liquid desiccant system gives the added benefit of being biocidal, neutralizing potential for mold growth.

Current ventilation requirements are 20cfm per person, although 40cfm is considered ideal for comfort, health and a feeling of well being. A ventilation rate of 0.3cfm/ft² would be 30% the conventional VAV air movement, but provide more ventilation air. Air could be introduced as a displacement ventilation system at low level or as a high level supply system with a low level exhaust. The cost of treating the extra air is minimal using ground source cooling, heating and humidity control through the desiccant system. The amount of air required for humidity control in the summer is 0.3cfm/ft² during high humidity conditions.

Because people are twice as sensitive to radiant temperature as they are to ambient temperature, temperature control is best accomplished by radiant sources to maximize occupant comfort. Radiant floors, ceilings, columns and external walls and columns are ideal thermal systems, accomplished by integrated water-bearing pipes. This integrates the cooling and heating system into the structure and uses the mass of the building as a heat sink and radiator. Ambient air temperature control can be assisted by the ventilation system. Using ground coupled cooling, we eliminate refrigeration equipment because we only need 60°F cooling water.

Heating and hot water are provided by low temperature hot water condensing boilers set for 120°F in the winter. Heating the structure through the midday period reduces the heating load. Radiant piping would be zoned for perimeter and core areas, which could allow core heat to be moved to the perimeter in the winter, further reducing the heating load. Using earth-coupled heat of 55°F in the winter for preheating the air minimizes the heating load. Maintaining even temperatures in the building requires much less heating. The size of the heating boilers is reduced by 75% to 2,000,000BTU/h boilers but 3,000,000 is required for dehumidification in the summer at a higher temperature of 180°F, which could be generated very efficiently by boilers or solar collectors.

This HVAC system uses 85% less energy for the distribution system, no refrigeration energy, and low temperature hot water condensing boilers running at 97% efficiency for heating and hot water. The piping and ducting systems provide maximum flexibility and adaptability. Personal temperature control is provided by personal heating/cooling through low temperature radiant panels, given to occupants as requested and connected into a separate piped distribution system that offers heat in the winter and cooling in the summer.

Table 1. Effects of Static and Dynamic Integration on HVAC Systems - 200,000FT² Office Block

	No Integration, VAV with Reheat, Standard System	Static Integration of VAV with Reheat	Static Int. & Some Dynamic Int. of an All Air System	Whole Building Dynamic Int. of a HVAC System
Sizing and Install Cost
Air System Size	1cfm/ft²	0.7cfm/ft²	0.6cfm/ft²	0.3cfm/ft²
Total Air Quantity	160,000cfm	112,000cfm	96,000cfm	48,000cfm
Pipework System	5Btu/ft²	10Btu/ft²	15Btu/ft²	25Btu/ft²
Total Cost of System	$2.3m	$2m	$2.3m	$3.6m
Mortgage $/ft²y	$1.15/ft²year	$1.00/ft²year	$1.15/ft²year	$1.80/ft²year
Annual Cost
Annual Energy Cost	$1.80/ft²year	$1.30/ft²year	$1.10/ft²year	$0.45/ft²year
Annual Maint & Op	$1.20/ft²year	$1.10/ft²year	$1.00/ft²year	$0.54/ft²year
Total Running Cost	$3.00/ft²year	$2.40/ft²year	$2.10/ft²year	$0.99/ft²year
Productivity Performance
Productivity Performance	Base Case	+0.5%	+1.5%	+8.0%
Productivity Worth	0	$1.25/ft²	$3.75/ft²	$20.00/ft²

Table 1 demonstrates the effect of static and dynamic integration on building HVAC system design, reducing the HVAC system energy consumption by over 70%, reducing maintenance by over 50% and increasing productivity by 8%. Installation cost of the dynamically integrated system is a worst-case scenario. The dynamic integration costs can be reduced to within 20% of a VAV system with close design integration.

Relevant Codes and Standards

• Energy Policy Act of 2005 (PDF 1.9 MB)
• ASHRAE Handbooks
• ASHRAE Energy-Efficient Design in New Buildings Series 90,
• ASHRAE Energy Conservation in Existing Buildings, Standard 100-2006
• 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 / Space Types

Applicable and relevant to all building types and space 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—HVAC Integration
Federal Green Construction Guide for Specifiers:

• 01 57 19.11 (01352) Indoor Air Quality (IAQ) Management
• 01 78 23 (01830) Operation and Maintenance Data
• 01 91 00 (01810) Commissioning
• 23 30 00 (15800) HVAC Air Distribution
• 23 70 00 (15700) Central HVAC Equipment

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.