The primary intent of this article is to provide guidelines for improving building energy efficiency and providing proper indoor environmental quality (e.g., thermal comfort, proper illumination, sufficient ventilation, acoustic performance) through an integrated design process and the proper selection of equipment and design parameters. A healthy and energy efficient environment is expected to improve occupant productivity as well.
Commercial buildings in the United States are major contributors to high energy usage. With growing demand for power, higher energy prices, and increased awareness of environmental issues, the need grows for sustainable energy management. We describe some proven methods and techniques to improve overall building performance, using our experience with the Texas Tech University Health Sciences Center. The listed strategies provide design, operation, and energy management plans that are beneficial for building owners. These guidelines and specifications are intended for campus and commercial building design and facility professionals.
Design Process and Methodology
For new building or major renovation projects, an integrated project design team shall be formed to include representatives from the owner, consultants, and contractors. The design target shall comply with any applicable standards (e.g., federal, state, owner), to integrate energy efficiency, resource conservation, water safety, land use, site development, indoor environmental quality, and building performance. Building design and construction shall take energy efficiency, service life, air tightness, water vapor management, and acoustics into consideration. Space, especially laboratories, shall be designed for flexibility, safety, and reliability. Leverage landscaping to provide natural shade for the building. Select plants that will conserve water.
All applicable codes and standards shall be adhered to when computing building peak cooling, heating, and ventilation loads. Based on our experience, a whole-building simulation software application can be used to accomplish this. Life-cycle cost and risk analyses shall be performed to select the make and model of chillers, boilers, pumps, fans, and other high energy-consuming equipment.
In addition to the mandatory requirements of energy codes and standards, the Energy Cost Budget (ECB) method shall be used to demonstrate energy compliance. We recommend the ECB method because it uses whole-building hourly energy simulation to optimize building parameters and equipment selection. All energy conservation measures shall be identified and incorporated in the architectural and engineering plans during the design development phase. A district or central heating and cooling system shall be designed for locations where the thermal load density and annual load factors are expected to be very high. Building automation control software shall be selected at an early stage, and a control professional shall be included in the project design team.
A lighting software package shall be used to demonstrate that each space meets illumination and lighting power density and distribution requirement. Commissioning shall be included in the project scope to ensure that system performance meets or exceeds design objectives and criteria. Assuming that renewable energy is cheaper than the alternative, it would be cost effective to encourage electric providers to include a substantial percentage of renewable energy in their fuel mix.
Typical Air Handling Unit
Based on a life-cycle cost (LCC) analysis, an air handling unit (AHU) with a dual duct system provides the lowest cost in most cases. For smaller size buildings, packaged air units with a heat pump option provide the lowest life-cycle cost. Variable refrigerant flow and chilled beam systems are recommended for certain space usage. Peak cooling, heating, and ventilation loads shall be determined using a whole-building simulation software package or other approved means.
Variable-flow fan array systems with direct-drive plenum fans have added benefits for medium to large size AHUs. Select fans that operate at highest efficiency at 80% of design flow. The direct digital-control system with fault detection and diagnostics will provide energy savings and fault correction quickly. High-efficiency cooling coils with industry-best thermal performance and least moisture carryover limits shall be installed.
The duct system shall be designed with proper sound attenuation to maintain acceptable sound level per the owner’s requirement. The cooling and heating water-flow control valves shall be pressure independent. A commissioning professional shall adjust and balance the flow, check the control algorithm, and report all measured data and identified deficiencies to the owner using an acceptable written format.
The AHU shall be programmable to accommodate for occupied, unoccupied, and holiday operations, to include economizer operation, unoccupied setup/setback temperature, discharge air duct static pressure reset, and demand control ventilation. The control system shall be monitored continuously for equipment operations, fault detection, and diagnostics.
Each variable air volume (VAV) box shall serve spaces of similar occupancy or space use. Comfort problems can arise if the air flow is below 75% of its maximum. The Air Diffusion Performance Index falls off rapidly at lower flow, which causes poor diffusion and comfort problems. Adequate air circulation will ensure proper mixing, adequate ventilation, less temperature stratification, good indoor air quality, and humidity control. Avoid aerodynamically generated noise in the diffusers. Diffusers shall be selected based on the manufacturer’s acoustic performance data.
For larger buildings, boilers shall be a modular system consisting of multiple smaller boilers. Condensing type boilers are preferred.
Chillers shall be sized and controlled to realize least operating cost at part loads. Centrifugal or screw type chillers, if selected, shall be of variable speed type. Chillers, if used, shall be sequenced to obtain the lowest operating cost to meet the building cooling demand. Cooling demand shall be based on real-time building load. Chiller efficiency shall be continuously monitored by the control system.
For larger buildings, boilers shall be a modular system consisting of multiple smaller boilers. Condensing type boilers are preferred. Non-condensing boilers, if selected, shall have flue heat recovery coils. The boiler(s) shall be tested and certified with high thermal efficiency and turndown ratio. Boiler efficiency and stack data shall be monitored continuously by the control system. The heating water temperature shall reset inversely with the outside air temperature. Domestic water heaters shall be condensing or heat pump type.
LED (light emitting diode) light fixtures with high efficacy and long life are recommended for use. Parking lot lights are recommended to dim 50% during lean occupancy period of the building at night (e.g., midnight to 5:00 am). Exterior lighting shall be controlled by a photocell. Indoor lighting shall be controlled by dual-technology occupancy sensors. Exceptions for certain types of occupancies per energy code are acceptable. Dimming controls with occupancy sensors are recommended for offices, classrooms, conference rooms, and laboratory spaces.
K-rated transformers are recommended for serving sensitive equipment and solid-state controls. Transformers serving research laboratories or similar spaces with substantial solid-state controls shall be rated K-13. All motors of 1 horsepower (hp) or higher shall be premium efficient type and be compatible with variable frequency drives (VFDs). VFDs for pumps and fans shall utilize harmonic filters. VFDs shall have a high power factor, less than 10% total harmonic distortion, and high MTBF (mean time between failures) years.
Energy Management and Awareness Plan
Energy efficiency provides the opportunity to save on energy costs, minimize emissions, and reduce per capita energy demand. A comprehensive energy management plan shall include monthly utility consumption and cost data, energy price risk assessment, energy audits, renewable energy opportunities, and energy conservation project identification and implementation. The most effective energy conservation techniques include utility data collection and analysis, energy benchmarking, whole-building energy simulation, detailed audits, commissioning, retrocommissioning, control system monitoring, fault detection and diagnostics, and building equipment performance.
Review all utility tariffs and ensure that the most favorable terms are realized. Perform detailed energy audits of the buildings and identify potential energy conservation projects. Finance and implement energy conservation projects with acceptable payback. Establish energy savings monitoring and an evaluation plan.
Keep abreast of new and proven technologies and apply these technologies where opportunities exist. Identify and take advantage of opportunities for reducing energy consumption, optimizing operations, and reducing operation and maintenance costs. Utilize specialized engineering consulting firms for retrocommissioning buildings. Ensure that all renovations and new building design and construction meet or exceed the most recent edition of the applicable energy conservation codes and that they utilize the most economic practices.
The Energy Awareness Plan shall include strategies to prevent waste and maintain a process of educating and communicating policies and best energy conservation practices to the occupants of the facilities.
Texas Tech University Health Sciences Center has buildings in six different locations in Texas. The design target was to meet the university’s Green Construction Standard, which integrates energy efficiency, resource conservation, water safety, land use, site development, indoor environmental quality, and building performance. For new buildings, we use most of the strategies described in the design process, methodologies, and recommendation sections above. For existing buildings, some of the energy conservation projects implemented are provided below. Copies of the reports can be provided on request. Building load simulations were done using TRACE 700 or 3Dplus software.
The design target was to meet the university’s Green Construction Standard, which integrates energy efficiency, resource conservation, water safety, land use, site development, indoor environmental quality, and building performance.
We used the net present worth method of LCC analysis at 2% interest rate over the expected service life per ASHRAE recommendations for cost justification of new equipment selection or replacement of existing. Flat rates for electricity ($0.075/kWh) and gas ($0.7/ccf) were used for cost analysis. The savings were established using the measurement and verification method after project implementation.
- High-efficient scroll or variable drive screw chillers are more expensive but provide payback in less than 20 years compared to standard chillers. Similar results were obtained by comparing variable drive electric centrifugal chillers with steam driven chillers.
- Life-cycle cost of dual duct air handling systems is marginally lower than single duct system with reheat, mainly due to lower maintenance cost.
- Use of condensing boilers for heating and domestic water reduced gas usage, but most of the cost savings are being realized due to lower maintenance cost and longer expected service life of stainless-steel construction.
- LED lighting retrofit with occupancy sensors provide payback in less than 5 years compared to fluorescent light fixtures. LED lighting provides cost-effective dimming and color tuning.
- Belimo pressure independent valves increased chilled water differential temperature up to 6°F. Higher differential reduced flow to the cooling coils. These valves provide precise flow control and compensate for pressure variations in the closed loop hydronic systems.
- The higher cost of premium efficient motors and K-rated transformers paid off within 5 years. In addition, these motors and transformers last longer due to better insulation. Rewinding motors up to 25 hp may not be worth it.
- AHUs with 2″ casing insulation reduced noise level from 95+dB to 52 dB at 5 feet from the unit.
- Replacement of damaged insulation on steam and condensate pipes was estimated to save up to $16/foot annually.
All the above recommendations will improve the whole-building performance over the service life expected of it. The design engineers/architects, building facilities personnel, and contractors are expected to provide best effort to implement the recommendations. Some strategies will have a higher initial costs but lower life-cycle costs.
Several tools and methods—such as whole-building energy simulation modeling using TRACE, lighting design using VisualPro, field measurement and verification, energy benchmarking analysis, control system monitoring, fault detection and diagnostics—were used by the primary author to implement these recommendations for university buildings with good results.
This article is based on knowledge obtained from training courses and books offered by the Association of Energy Engineers (AEE) and the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and lessons learned from subsequent implementation of energy conservation strategies at Texas Tech University Health Sciences Center.
Amiya Panigrahi is an engineer with Texas Tech University Health Sciences Center in Lubbock, TX. He can be reached at [email protected]. Indu Panigrahi is an undergraduate in the Department of Computer Science and the Department of Geosciences at Princeton University in Princeton, NJ. This is their first article for Facilities Manager.