The following review provides a brief reference to key considerations with some of the most efficient technologies. As with lighting, test installations are a good idea; therefore working with manufacturers and distributors.
Gaining maximum efficiency from HVAC controls
Since building performance can be greatly improved by installing and fully using HVAC controls, it is important to understand and properly use these controls. A place to start is to carefully look at what is really happening in your building, 24 hours a day, seven days a week.
What happens with each equipment? On the weekend? Weekend? How does the time of year change, have your operations changed? It is important to understand where and how energy is consumed in order to determine where waste occurs and where improvements can be realized. Then you need to ask: “What exactly do I want these controls to do?”
Energy management systems (EMS) are designed to more efficiently use individual pieces of equipment and ensure equipment integration, improve system efficiency. In a typical EMS, sensors monitor parameters such as air and water temperature, pressure, humidity, flow, and energy consumption. From these execution points, the operating time and the set points of the electrical and mechanical equipment are monitored.
Seven-day planning provides hourly and daily management of HVAC systems and lighting, and may take into account holiday and seasonal changes. As the name implies, the night temperature stop allows less cooling in the summer and less heating in the winter in unoccupied hours.
Optimal start / stop allows the entire system to look ahead for several hours and, depending on current conditions, make decisions about how to act; This allows the system to grow slowly, avoiding surges in demand or unnecessary work time.
Peak demand for electricity can be controlled by switching on fans and pumps in order to start one after the other, not immediately, and in a short time to turn off pieces of HVAC equipment (up to 30 minutes), which should only minimally affect the space temperature. Economists reduce cooling costs by using cold outside air. Resetting the supply air temperature can prevent excessive heat and reduce the load on the chiller.
EMS can provide a lot of information about the performance of a building, but someone has to figure out what they want to do with EMS and then give them directions. Control calibration, testing and balancing are key to any well-supported HVAC system, but are especially important for optimizing control efforts.
Variable speed drives and energy efficient motors
Variable speed drives (VSD) are almost always recommended as a reliable and economical upgrade.
VSDs are beneficial where equipment is large or often operates under partial load conditions. Savings of up to 70 percent can be achieved by installing frequency converters on fan motors operating under partial load conditions. They can be applied to compressor or pump engines and are commonly used in systems with a variable air volume (VAV). They are also cost effective in water intakes. Inclined and air fans are the best candidates for VSD.
Duct configurations controlled by variable inlet vanes or outlet dampers transmit energy under partial load conditions. Using throttle valves to reduce flow for small pumping loads is also inefficient. Engine efficiency begins to decline dramatically when they operate at less than 75 percent of full load; they can consume two times more energy than the load required. VSDs work electronically and continuously adjust the engine speed to match the load.
The power to run VSD is proportional to the cube of speed (or flow), so this technology is so efficient. If the rate drops by only 10 percent, this should result in a 27 percent reduction in energy consumption. An experimental VSD study conducted by the EPA showed that the VSD modification implemented annual average energy savings of 52 percent, average demand savings of 27 percent, and 2.5-year payback.
Perform harmonics, power factor, electrical load and torsional analysis before selecting a frequency converter. Although problems with harmonics and power factor are not common in VSD applications, VSDs usually must be equipped with integral harmonic filters (or a three-phase AC line reactor) and internal power factor correction capacitors (or one capacitor per VSD transmission line). In general, this equipment is not standard and should be specified.
Improved design and better materials increase the performance of energy-efficient engines, which consume 3-8% less energy than standard engines; units with an efficiency of 95%.
To achieve maximum savings, the motor must also be appropriately matched to the load, increasing the running time with maximum efficiency. Engines work best with 75 to 100 percent of their full rated load; Engines operating at a frequency below 60 percent of their rated capacity are prime candidates for modernization. For engines whose loads fluctuate, VSD should also be considered.
Smaller, more efficient engines are an integral part of the system, reducing the scale; Reducing a standard 75 horsepower engine to a 40-horsepower, energy-efficient model will result in energy savings of 15 percent.
Some energy-efficient engines have less “slippage” than engines with normal performance, which leads to the fact that energy-saving engines operate at slightly higher speeds; consider a larger pulley to compensate for higher speed and maximize energy savings. Installing a new pulley or customizing an existing one can be an alternative to VSD when the cost of the VSD is prohibitive or the load is reduced.
Improve fan system performance
A common way to increase the efficiency of an air distribution system is to convert a constant air volume (CAV) system to VAV. One energy authority, E-Source, reports that "typical (VAV) airflow requirements are only about 60 percent of the total CAV flow."
VAVs respond to load requirements by changing the volume of air through a combination of pressure regulators and dampers, rather than changing the air temperature. In accordance with the air pressure, the fan power and the volume of the conditioned air are reduced, which increases the energy efficiency. Of course, it is very important to maintain indoor air quality (IAQ) when changing ventilation systems.
To maximize savings, VAV components such as VSD, variable pitch fan blades, diffusers, mixers, and VAV boxes should work correctly; VAV optimization also requires careful zoning.
E-Source recommends that you consider the following procedures for upgrading VAV:
• comprehensive measures to reduce the load and the calculation of the maximum and minimum requirements for air flow,
• measurement of existing fan characteristics; examine the duct system for possible improvements,
• phase fans, which are in parallel configurations,
• systematize the system,
• optimize the static pressure setpoint and reset, and
• It is possible to remove fans with return air.
Energy-efficient and suitable-sized engines are also recommended, as well as careful control strategies. Installing an autonomous device with thermal power to each diffuser can increase control over VAV systems by controlling individual spaces rather than infinite zones, and eliminate the need for VAV boxes. Such a device also offers VAV-style features for CAV-systems.
The cost of VAV upgrades and payback can vary widely. Installation problems associated with fan control, reduced supply air distribution, the location of pressure sensors and their reliability, in addition to insufficient design, can reduce the performance of a VAV modification. Since VAV boxes are securely expensive and necessary for each zone, it is usually impractical to divide the space into many zones. Careful design of the zone - depending on occupancy, internal loads and solar gain - will provide maximum efficiency, increase comfort and reduce reheating.
When reheating cannot be eliminated, consider these steps to minimize it: ensuring thermostat calibration; an increase in the supply air temperature during the cooling season; and monitoring of reheating all year round and possibly the use of reheating only during the winter months. In cases where preheating is mainly used to control humidity, a desiccant wheel or heat pipe can be considered.
Reducing existing VAV fan systems is a relatively inexpensive way to save energy when the load is reduced or from the beginning, when the air distribution system was increased. The following are ways to reduce fan consumption or airflow requirements:
• Reduce the static pressure set point to meet actual temperature and air flow requirements.
• Allow engines and upgrade them to energy efficient models; install larger pulleys.
• Replace the existing fan pulley with a larger one; which will reduce the fan power, reducing its speed.
• Ensure that the fan speed matches the load. Reducing the fan speed by 20 percent reduces energy consumption by about 50 percent.
There are several ways to determine whether large fans have a VAV system. If the measured motor current is 25 percent less than its nominal price, it is large. If the intake fan blades or exhaust dampers are closed by more than 20 percent, it is oversized. If the static pressure reading is less than the static pressure setpoint when the inlets or dampers are opened, and the VAV boxes open 100%, like on a hot summer day, the system is large. Again, be sure to consider IAQ requirements when reducing air conditioning systems.
Chillers and thermal storage
No one wants to replace a perfectly good chiller just because of the phasing out of CFCs. But after the load reduction efficiency upgrade is complete, it may actually be beneficial to replace an oversized chiller. This is especially true given the rising prices and the tightening of the supply of CFC refrigerants.
Oversized units of 10 years and older are good candidates for substitution. The high-performance chiller reduces energy costs over the entire life cycle; initial costs are reduced, because the replacement of the chiller is less than before. Depending on the efficiency and load of the old unit, the energy consumption of a highly efficient chiller can be from 15 to 30 kW / t less, which reduces energy consumption by 85 percent, combined with a reduction.
An alternative to replacement is to upgrade the chillers to accommodate the new refrigerant and to meet reduced loads. This may lead to the replacement of the diaphragm, replacement of the impeller, and possibly replacement of the compressor, depending on the characteristics of the chiller.
Upgrading may entail replacing gaskets and seals and rewinding the engine. Depending on the refrigerant and the method of modernization, the chiller may lose either efficiency or power. To determine if a replacement or upgrade is the best option, consider both the initial and living costs.
The recovery of the condenser and the evaporator provides significant energy savings, but if it makes sense, given its high cost, it depends on the condition of the chiller. Water cooled condensers are usually more efficient than air cooled devices. As condenser water flows through an open circuit, it is prone to contamination. Scale-up will interfere with heat transfer efficiency; therefore, maintenance is required to keep the surface clean.
Absorption chillers are an alternative to centrifugal models. Absorption chillers cost up to $ 150 per ton more than steam compressors, such as centrifugal units, but can be profitable in areas with high energy costs or where there is steam or gas, depending on local utility tariff structures. Using a combination of two types of chillers can reduce energy costs.
The heat storage facility (TES) uses traditional equipment for chillers to produce conditioned water or ice (or sometimes other material with a phase change) during off-peak periods. Water is discharged from storage during the day or during peak hours and circulates through the cooling system.
TES systems can be incorporated into new and existing systems and can provide partial load balancing or full load bias. TES helps reduce operating and maintenance costs; in some cases a small chiller may be indicated. Some systems provide lower supply air and water temperatures, so air and water consumption can be reduced.
Water side improvement
Material filling, size and fan configurations affect the efficiency of the cooling tower. Cellular fill (aka film) increases efficiency compared to other types of filling. An oversized tower providing a closer approach to ambient temperature can increase its efficiency. Generous calibration of the tower and an increase in its share of the load on the chiller can make economic sense, since the initial cost and consumption of the cooling tower is a ton less than the chiller.
Under partial load conditions, applying a frequency converter to a fan (or pump) will improve the efficiency of the tower. Systems with VSD and multiple fans are more efficient when all cellular cells operate at a reduced speed, unlike one or two cells at full speed.
Because cooling towers contain large heat exchange surfaces, pollution or increased mucus can be a problem. The effectiveness of improperly treated systems can be improved with effective water treatment. High performance towers available; types with scribbled sediments are more popular and effective than tower towers. Performance can also be improved by increasing the surface area of the cooling.
In traditional pumping systems, flow is usually constant volume; a throttle valve reduces flow under partial load conditions, which reduces efficiency.
Installing frequency converters on secondary pumps in variable flow systems, using pumps and motors to meet load requirements, and upgrading single-loop systems to primary / secondary circuit configurations can improve the performance and reliability of pumping systems. When modernizing chilled water pumps, it is important to ensure maximum and minimum flow rates through the chiller.
Other cooling options
Dehumidifiers are dehumidification materials that can be integrated into HVAC systems to reduce cooling loads and increase chiller efficiency, improving quality and comfort in the room. Previously found only in niche and industrial applications, dehumidifier cooling is distributed through commercial markets.
Dehumidifiers make sense when their regeneration costs are low compared to the costs of dehumidification below the dew point and in some cases can reduce HVAC energy and peak demand by more than 50 percent.
Evaporative coolers provide one of the most economical and efficient methods of cooling, using 75 percent less energy than vapor compression systems. Although the initial cost is usually higher, the payback for evaporative coolers ranges from six months to five years. Although evaporative coolers are especially common in the arid west and southwest, they can serve most US climates. E-Source утверждает, что в сочетании с испарительным охлаждением охлаждение осушителем может исключить охлаждение кондиционирования воздуха во многих климатах.
Гибридные системы, которые интегрируют испарительное охлаждение с использованием традиционных технологий HVAC, предоставляют дополнительные возможности. Для повышения производительности рассмотрите более низкую скорость воздуха; лучше заполнять материалы; более высокая эффективность вентиляторов, насосов и двигателей, включая преобразователи частоты; лучшие ремни или прямой привод; улучшенное жилье; улучшенные средства управления; и уплотнение канала. Правильное техническое обслуживание является ключевым фактором энергоэффективности.
Упакованные кондиционеры обычно находятся в зданиях или зонах зданий, где охлаждающая нагрузка составляет менее 75 тонн. Запуск этих устройств при частичной нагрузке может серьезно снизить эффективность. Они, как правило, не так эффективны, как чиллерные системы, но могут быть обновлены и защищены при замене. Существующие системы могут быть улучшены за счет использования более высокоэффективных компрессоров, более крупных конденсаторов и испарителей и преобразователей частоты, хотя ожидаемая продолжительность жизни от 10 до 12 лет для этих технологий может означать, что модернизация не является экономически эффективной.
Тепловые насосы являются одними из самых энергоэффективных технологий отопления и охлаждения, доступных сегодня. Низкие эксплуатационные расходы, повышенная надежность и длительный срок службы улучшают их ответственность. Они лучше всего функционируют в умеренном климате, и правильная калибровка имеет решающее значение.
Многоуровневые конфигурации могут обслуживать большие нагрузки и обеспечивать зонирование; крупные, модернизированные центральные подразделения, предлагающие мощности до 1000 лошадиных сил или 750 киловатт, набирают популярность. Тепловые насосы типа воздух-воздух являются наиболее распространенными из-за низких начальных затрат; тепловые насосы наземного питания являются наиболее эффективными, но, как правило, имеют более высокие первоначальные затраты.
Модернизация котла
Особенно в более холодных климатах улучшенная производительность котла - с улучшенным управлением топливом и воздушным потоком в различных условиях нагрузки и повышенной площадью поверхности теплопередачи - может существенно способствовать экономии энергии. Меньшие узлы, размещенные в модульных системах, повышают эффективность до 85 процентов, а небольшие единицы, заменяющие системы с разомкнутым контуром, снижают эффективность сгорания до 95 процентов.
Модернизация котла в сочетании с улучшенными мерами технического обслуживания также может повысить эффективность - до 90 процентов. Новые горелки, дефлекторные вставки, регуляторы горения, системы контроля теплой погоды, экономайзеры, рекуперация тепла и конверсия конденсата обеспечивают повышенную эффективность. Небольшой «летний» котел может быть хорошим вариантом, когда котел требуется круглый год, хотя при меньших емкостях в более теплых условиях. Гораздо меньший летний котел рассчитан на снижение нагрузки; главный котел отключается.
Модернизация HVAC может обеспечить огромные экономические выгоды, улучшить комфорт для пассажиров и надежность системы и снизить эксплуатационные расходы. Но чтобы максимизировать выгоды и свести к минимуму капиталовложения, меры по снижению нагрузки, такие как обновление освещения, должны предшествовать модернизации системы HVAC.
