Energy efficiency and hvac technology

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Energy Efficiency And HVAC Technology
Understanding the interdependence of HVAC technologies with one another, as well as with other electrical loads and maintenance and operations practices, is integral to specifying individual HVAC technologies and whole systems. As with lighting, technologies and possible configurations for HVAC systems are vast and varied.
The following overview offers a quick reference to key considerations with some of the most effective technologies. As with lighting, trial installations are a good idea; so is working with manufacturers and distributors.
Getting the most from HVAC controls
Because a building's performance can be dramatically improved by installing and fully using HVAC controls, it is essential to understand and correctly use those controls. The place to start is with a close look at what is really transpiring in your building, 24 hours a day, seven days a week.
What is happening with each piece of equipment? On holidays? Weekends? As the seasons change, do your operations change? It is important to understand where and how energy is being consumed in order to identify where waste is occurring and where improvements can be implemented. Then it is imperative to ask, "What exactly do I want these controls to do?"
Energy management systems (EMS) are designed to run individual pieces of equipment more efficiently and to permit integration of equipment, enhancing performance of the system. In a typical EMS, sensors monitor parameters such as air and water temperatures, pressures, humidity levels, flow rates, and power consumption. From those performance points, electrical and mechanical equipment run times and setpoints are controlled.
Seven-day scheduling provides hour-to-hour and day-to-day control of HVAC and lighting systems and can account for holidays and seasonal changes. As the name implies, night temperature setback allows for less cooling in summer and less heating in winter during unoccupied hours.
Optimal start/stop enables the entire system to look ahead several hours and, relative to current conditions, make decisions about how to proceed; this allows the system to ramp up slowly, avoiding morning demand spikes or unnecessary run times.
Peak electrical demand can be controlled by sequencing fans and pumps to start up one by one rather than all at once and by shutting off pieces of HVAC equipment for short periods (up to 30 minutes), which should only minimally affect space temperature. Economizers reduce cooling costs by taking advantage of cool outdoor air. Supply-air temperature-reset can prevent excessive reheat and help reduce chiller load.
An EMS can provide an abundance of information about building performance, but someone has to figure out what they want the EMS to do and then give it directions. Calibrating controls, testing and balancing are key to any well-maintained HVAC system, but are especially critical to optimize control efforts.
Variable speed drives and energy-efficient motors
Variable speed drives (VSDs) are nearly always recommended as a reliable and cost-effective upgrade.
VSDs are profitable where equipment is oversized or frequently operates at part-load conditions. Savings of up to 70 percent can be achieved by installing VSDs on fan motors operating at part-load conditions. They may be applied to compressor or pump motors and are generally used in variable air volume (VAV) systems. They are also cost effective in water-side applications. Backward-inclined and airfoiled fans are the best VSD candidates.
Air-handler configurations controlled by variable inlet vanes or outlet dampers squander energy at part-load conditions. Using throttle valves to reduce flow for smaller pumping loads is also inefficient. The efficiency of motors begins to drop off steeply when they run at less than 75 percent of full load; they can consume over twice as much power as the load requires. VSDs operate electronically and continually adjust motor

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Energy efficiency and hvac technology

  1. 1. Energy Efficiency And HVAC TechnologyUnderstanding the interdependence of HVAC technologies with one another, as well as with otherelectrical loads and maintenance and operations practices, is integral to specifying individual HVACtechnologies and whole systems. As with lighting, technologies and possible configurations for HVACsystems are vast and varied.The following overview offers a quick reference to key considerations with some of the mosteffective technologies. As with lighting, trial installations are a good idea; so is working withmanufacturers and distributors.Getting the most from HVAC controlsBecause a buildings performance can be dramatically improved by installing and fully usingHVAC controls, it is essential to understand and correctly use those controls. The place to start iswith a close look at what is really transpiring in your building, 24 hours a day, seven days aweek.What is happening with each piece of equipment? On holidays? Weekends? As the seasonschange, do your operations change? It is important to understand where and how energy is beingconsumed in order to identify where waste is occurring and where improvements can beimplemented. Then it is imperative to ask, "What exactly do I want these controls to do?"Energy management systems (EMS) are designed to run individual pieces of equipment moreefficiently and to permit integration of equipment, enhancing performance of the system. In atypical EMS, sensors monitor parameters such as air and water temperatures, pressures, humiditylevels, flow rates, and power consumption. From those performance points, electrical andmechanical equipment run times and setpoints are controlled.Seven-day scheduling provides hour-to-hour and day-to-day control of HVAC and lightingsystems and can account for holidays and seasonal changes. As the name implies, nighttemperature setback allows for less cooling in summer and less heating in winter duringunoccupied hours.
  2. 2. Optimal start/stop enables the entire system to look ahead several hours and, relative to currentconditions, make decisions about how to proceed; this allows the system to ramp up slowly,avoiding morning demand spikes or unnecessary run times.Peak electrical demand can be controlled by sequencing fans and pumps to start up one by onerather than all at once and by shutting off pieces of HVAC equipment for short periods (up to 30minutes), which should only minimally affect space temperature. Economizers reduce coolingcosts by taking advantage of cool outdoor air. Supply-air temperature-reset can prevent excessivereheat and help reduce chiller load.An EMS can provide an abundance of information about building performance, but someone hasto figure out what they want the EMS to do and then give it directions. Calibrating controls,testing and balancing are key to any well-maintained HVAC system, but are especially critical tooptimize control efforts.Variable speed drives and energy-efficient motorsVariable speed drives (VSDs) are nearly always recommended as a reliable and cost-effectiveupgrade.VSDs are profitable where equipment is oversized or frequently operates at part-load conditions.Savings of up to 70 percent can be achieved by installing VSDs on fan motors operating at part-load conditions. They may be applied to compressor or pump motors and are generally used invariable air volume (VAV) systems. They are also cost effective in water-side applications.Backward-inclined and airfoiled fans are the best VSD candidates.Air-handler configurations controlled by variable inlet vanes or outlet dampers squander energyat part-load conditions. Using throttle valves to reduce flow for smaller pumping loads is alsoinefficient. The efficiency of motors begins to drop off steeply when they run at less than 75percent of full load; they can consume over twice as much power as the load requires. VSDsoperate electronically and continually adjust motor speed to match load.The power to run the VSD is proportional to the cube of the speed (or flow), which is why thistechnology is so efficient. If the speed is reduced by just 10 percent, a 27 percent drop in powerconsumption should result. A VSD pilot study performed by EPA found that VSD retrofitsrealized an annual average energy savings of 52 percent, an average demand savings of 27percent and a 2.5-year simple payback.Perform harmonic, power factor, electric load, and torsional analyses before selecting a VSD.Though harmonic and power factor problems are not common in VSD applications, VSDsshould generally be equipped with integral harmonic filters (or a three-phase AC line reactor)and internal power factor correction capacitors (or a single capacitor on the VSDs main powerline). In general, this equipment is not standard and must be specified.
  3. 3. Improved design and better materials enhance the performance of energy-efficient motors, whichuse 3 to 8 percent less energy than standard motors; units with efficiencies of 95 percent areavailable.To achieve maximum savings, the motor must also be properly matched with its load, increasingrun time at peak efficiency. Motors operate best when running at 75 to 100 percent of their fullyrated load; motors routinely operating below 60 percent of rated capacity are prime candidatesfor retrofit. For motors whose loads fluctuate, VSDs should also be considered.Smaller, more efficient motors are integral to a system downsizing stratagem; downsizing a 75horsepower standard motor to a 40 horsepower energy-efficient model will result in energysavings of 15 percent.Some energy-efficient motors have less "slip" than standard-efficiency motors, causing energy-efficient motors to run at slightly higher speeds; consider a larger pulley to compensate for thehigher speed and to maximize energy savings. Installing a new pulley or adjusting the existingone can also be an alternative to a VSD when the cost for the VSD is prohibitive or the load hasbeen reduced.Improving fan system performanceA common way to improve the efficiency of the air distribution system is to convert constant airvolume (CAV) systems to VAV. One authority on energy issues, E-Source, reports that "typical(VAV) air flow requirements are only about 60 percent of full CAV flow."VAVs respond to load requirements by varying the volume of the air through a combination ofpressure controls and dampers rather than by varying the airs temperature. According to the airpressure, fan power and volume of conditioned air are reduced, thus increasing energyefficiency. Of course, it is crucial to maintain indoor air quality (IAQ) when altering air handlingsystems.To maximize savings, VAV components such as VSDs, variable-pitch fan blades, diffusers,mixers, and VAV boxes must be operating properly; careful zoning is also required to achieveVAV optimization.E-Source recommends considering the following VAV retrofit procedures:• complete load reduction measures and calculate the maximum and minimum air flowrequirements,• measure existing fan performance; examine duct system for possible improvements,• stage fans that are in parallel configurations,• commission the system thoroughly,• optimize static pressure setpoint and implement reset control, and• possibly remove return air fans.
  4. 4. Energy-efficient and properly sized motors are also recommended along with careful controlstrategies. Installing a self-contained, thermally powered device to each diffuser can add greatercontrol to VAV systems by controlling individual spaces, rather than entire zones, and eliminatethe need for VAV boxes. Such a device also offers VAV-style capabilities to CAV systems.VAV retrofit costs and paybacks can vary widely. Installation problems related to fan control,reduced supply air distribution, location of pressure sensors and their reliability, in addition todeficient design, can diminish a VAV retrofits performance. Because VAV boxes are relativelyexpensive and one is required for each zone, it is generally not cost effective to partition thespace into many zones. Careful zone designation -- according to occupancy, internal loads andsolar gain -- will maximize efficiency, increase comfort and reduce reheat.When reheat cannot be eliminated, consider these steps to minimize it: ensuring thermostatcalibration; increasing supply air temperatures during the cooling season; and monitoring reheatyear round and possibly employing reheat only during winter months. Where reheat is usedprimarily to control humidity, a desiccant wheel or a heat pipe might be considered.Downsizing existing VAV fan systems is a relatively low-cost way to save energy when loadshave been reduced or when the air distribution system was oversized to begin with. Thefollowing are means to downsize fans or airflow requirements:• Reduce static pressure setpoint to meet actual temperature and airflow requirements.• Rightsize motors and upgrade to energy-efficient models; install larger pulleys.• Replace the existing fan pulley with a larger one; that will reduce the fans power requirementsby reducing its speed.• Make sure the fans speed corresponds to the load. Reducing a fans speed by 20 percentreduces its energy consumption by approximately 50 percent.There are several ways to determine if VAV fan systems are oversized. If a motors measuredamperage is 25 percent less than its nameplate rating, it is oversized. If a fans inlet vanes oroutlet dampers are closed more than 20 percent, it is oversized. If the static pressure reading isless than the static pressure setpoint when inlets or dampers are open and VAV boxes open 100percent, as on a hot summer day, the system is oversized. Again, be sure to consider IAQrequirements when downsizing air handling systems.Chillers and thermal storageNo one wants to replace a perfectly good chiller just because of the CFC phaseout. But onceload-reducing efficiency upgrades have been completed, it may actually be profitable to replacean oversized chiller. Thats especially true given rising prices and tightening supplies of CFCrefrigerants.Oversized units 10 years or older are good candidates for replacement. A high-efficiency chillerreduces energy costs throughout its lifetime; initial costs are reduced because the replacementchiller is smaller than the old one. Depending on the old units efficiency and load, a high-
  5. 5. efficiency chillers energy consumption can be.15 to.30 kW/ton less, decreasing energyconsumption by as much as 85 percent if combined with downsizing.An alternative to replacement is to retrofit chillers to accommodate a new refrigerant and tomatch reduced loads. That may involve orifice plate replacement, impeller replacement andpossibly compressor replacement, depending on the chillers specifics.Retrofitting may entail gasket and seal replacement and motor rewinding. Depending on therefrigerant and the way the retrofit is performed, the chiller may lose either efficiency orcapacity. To determine whether replacement or retrofit is a better option, consider both initialand life-cycle costs.Retubing the condenser and evaporator yields sizable energy savings but whether it makes sense,given its high cost, depends on the condition of the chiller. Water-cooled condensers aregenerally more efficient than air-cooled units. Because condenser water flows through an openloop, it is susceptible to fouling. Scale build-up will inhibit heat transfer efficiency; maintenanceis therefore required to keep the surfaces clean.Absorption chillers are an alternative to centrifugal models. Absorption chillers cost up to $150per ton more than vapor compression chillers like centrifugal units, but can be profitable in areasof high electrical demand charges or where steam or gas is available, depending on the localutility rate structures. Using a combination of the two chiller types can reduce electrical demandcharges.Thermal energy storage (TES) uses conventional chiller equipment to produce conditioned wateror ice (or occasionally another phase-change material) in off-peak periods. Water is withdrawnfrom storage during the day or at peak hours and circulated through the cooling system.TES systems can be incorporated into new and existing systems and can provide partial loadleveling or full load shifting. TES helps decrease operating and maintenance costs; in somecases, a smaller chiller can be specified. Some systems provide lower supply air and watertemperatures, so air and water flow requirements can be cut.Water-side improvementsFill material, size and fan configurations affect cooling tower efficiency. Cellular fill (aka filmpacking) increases efficiency over other fill types. Oversizing the tower to allow for closerapproach to ambient wetbulb temperature can improve its efficiency. Generously sizing thetower and increasing its share of the chiller load can make economic sense because a coolingtowers initial cost and energy use per ton are less than a chillers.At part-load conditions, applying a VSD to the fan (or pump) will improve the towers efficiency.Systems with VSDs and several fans are more efficient when all tower cells are operating atreduced speed as opposed to one or two cells at full speed.
  6. 6. Because cooling towers contain large heat exchange surfaces, fouling -- scale or slime build-up-- can be a problem. The efficiency of improperly treated systems can be improved with effectivewater treatment. High-efficiency towers are available; induced-draft types are more popular andefficient than forced-draft towers. Performance can also be improved by increasing coolingsurface area.In traditional pumping systems, flow is generally constant volume; a throttle valve reduces flowat part-load conditions, inhibiting efficiency.Installing VSDs on secondary pumps in variable flow systems, rightsizing pumps and motors tomeet load requirements, and upgrading single loop systems to primary/secondary loopconfigurations can increase the performance and reliability of pumping systems. In upgradingchilled water pumps, it is important to meet maximum and minimum flow rates through thechiller.Other cooling optionsDesiccants are dehumidification materials which can be integrated into HVAC systems to reducecooling loads and increase chiller efficiency while improving indoor air quality and comfort.Formerly found only in niche and industrial applications, desiccant cooling is extendingthroughout commercial markets.Desiccants make sense when the cost to regenerate them is low compared to the cost todehumidify below dewpoint and can reduce HVAC energy and peak demand by more than 50percent in some cases.Evaporative coolers provide one of the most economical and efficient means of cooling, using upto 75 percent less energy than vapor-compression systems. Though initial cost is typicallyhigher, paybacks for evaporative coolers range between six months and five years. Thoughevaporative coolers are particularly prevalent in the arid West and Southwest, they can servicemost U.S. climates. E-Source states that, in combination with evaporative cooling, desiccantcooling can eliminate refrigerative air conditioning in many climates.Hybrid systems that integrate evaporative cooling with conventional HVAC technologies offeradditional opportunities. To improve performance consider lower air velocity; better fillmaterials; higher fan, pump and motor efficiencies, including VSDs; better belts or direct drive;improved housing; improved controls; and duct sealing. Proper maintenance is key to energy-efficiency.Packaged air-conditioning units are typically found in buildings or building zones where thecooling load is less than 75 tons. Running these units at part load can severely reduce efficiency.They are generally not as efficient as chiller systems but can be upgraded and rightsized whenreplaced. Existing systems can be improved by using higher efficiency compressors, largercondensers and evaporators, and VSDs, though life expectancies of 10 to 12 years for thesetechnologies may mean that retrofits are not cost-effective.
  7. 7. Heat pumps are among the most energy-efficient heating and cooling technologies availabletoday. Low operating costs, increased reliability and long life expectancies improve theirviability. They function best in moderate climates and proper sizing is critical.Multi-unit configurations can service larger loads and provide zoning; large, modernized centralunits offering capacities of up to 1000 horsepower or 750 kilowatts are gaining popularity. Air-to-air type heat pumps are the most common because of low up-front costs; ground supply heatpumps are the most efficient but tend to have higher initial costs.Boiler upgradesEspecially in colder climates, improved boiler performance -- with improved fuel and airflowcontrols over a range of load conditions and increased heat transfer surface areas -- cancontribute substantially to energy savings. Smaller units arranged in modular systems increaseefficiency up to 85 percent while small units replacing those with open-loop condensing systemsshoot combustion efficiency up to 95 percent.Boiler retrofits, combined with improved maintenance measures, can also increase efficiency --up to 90 percent. New burners, baffle inserts, combustion controls, warm-weather controls,economizers, blowdown heat recovery and condensate return conversions provide increasedefficiency opportunities. A smaller "summer" boiler might be a good option when a boiler isrequired year round though at reduced capacities in warmer conditions. The much smallersummer boiler is sized for reduced loads; the main boiler is shut down.HVAC upgrades can provide tremendous economic benefits, improve occupant comfort andsystem reliability, and reduce operating costs. But to maximize benefits and minimize capitalinvestment, load-reducing measures, such as lighting upgrades, should precede HVAC systemupgrades.Julian Arhire is a Manager with DtiCorp.com - DtiCorp.com carries more than 35,000HVAC products, including industrial, commercial and residential parts and equipmentfrom Honeywell, Johnson Contols, Robertshaw, Jandy, Grundfos, Armstrong and more.

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