By Daniel P. Duffy
It is said that the ultimate state of anonymity is achieved by the offensive linemen who battle in the trenches of professional football. These men never achieve the glory and recognition of the quarterbacks, receivers, and runners that they block for. Nobody ever notices that they are there . . . at least until they miss a block on a key play. Then, the eyes of the entire sports world are focused on them. A properly operating heating, ventilating, and air-conditioning (HVAC) system is a lot like a football lineman. When it is running perfectly, you don’t even know it is there. Recent advances in efficiency, operating controls, durability, and “smart” applications can make your HVAC system even more unnoticeable.
Basics of HVAC System Operation
Basic to the operation of any HVAC system is the difference between “sensible” heat and “latent” heat. Of the two, sensible heat is the one we deal with most often day to day. Sensible heat measures how hot something feels to the touch. It is quantified by measurement with a thermometer in degrees of heat (either using the Fahrenheit or Celsius scales).
Latent heat, on the other hand, measures the amount of heat energy transferred to or from a substance. For HVAC systems, this substance is usually a fluid (water, air, or some other gas like Freon) circulating in an enclosed loop system of pipes. As the fluid circulates, it repeatedly radiates and absorbs heat energy. As heat energy is absorbed by the fluid, it cools its surrounding environment as it warms the fluid. Conversely, heat energy radiated away from the fluid warms its surrounding environment as it cools the fluid. These simple transfers of heat are the basis of all heating, air-conditioning, and refrigeration systems.
Latent heat is measured in British Thermal Units (BTUs). A BTU is defined as the amount of energy needed to cool or heat one pound of water by 1°F. (Its metric counterpart is the joule.) So, 100 BTUs could be equal to the heat needed to raise the temperature 1 pound of water by 100 degrees, or to raise the temperature 100 pounds of water by 1 degree. A baseline heat value for measuring HVAC systems is 970 BTUs. This is referred to as the “latent heat of evaporation” of water since this is the amount of energy required to evaporate 1 pound of water into steam. Conversely, as steam condenses back into water, it releases 970 BTUs.
As a measurement of heat, BTUs are applicable to other fluids, including refrigerants like Freon, which have a lower boiling point than water, and therefore require fewer BTUs to cause evaporation. Freon is a registered trademark that includes a number of halocarbon liquids that are used as refrigerants, with each type or mix usually defined with an “R” followed by a numerical designation.
The refrigeration cycle used by air-conditioning systems is a four-step process that circulates the refrigerant from a low-pressure side of the loop to a high-pressure side, and back again. The refrigerant enters the evaporator as a liquid with lower pressure and lower temperature. It leaves the evaporator as a gas with lower pressure and higher temperature. The evaporator is a coil of piping connected to an air handler that blows indoor air across it. Heat from the surrounding air is transferred to the refrigerant, which then evaporates into a low-pressure gas. In doing so, the loss of heat cools the surrounding air, providing air conditioning to the inhabitants.
The refrigerant then enters the compressor and leaves as a gas with higher pressure and higher temperature. The compressor is a pump that provides the mechanical force needed to circulate the refrigerant through the system and drives the entire air-conditioning operation. There are several types of compressors (reciprocating, rotary, screw, or centrifugal) with differing capacities. The rated capacity is referred to as its “BTU rating,” and it will vary depending on the volume of refrigerant, the operating temperature of the evaporator, and the chemical characteristics of the refrigerant. Compressing this gas raises the pressure of the refrigerant.
The refrigerant then enters the condenser and leaves as a liquid with higher pressure and lower temperature. Like the evaporator, the condenser is a series of pipes which has air blown across it by a fan. But instead, heat is radiated from the refrigerant, and it condenses back into a liquid. For air-conditioning systems, the condenser is located outside the building being air conditioned, and the heat is radiated to the outside air.
The refrigerant then enters the expansion valve and leaves as a liquid with lower pressure and lower temperature. As it senses the temperatures of the evaporator and condenser, the expansion valve allows the liquid to pass through an orifice opening, which transforms the refrigerant into a low pressure, low temperature liquid. From the evaporation valve it circulates back to the evaporator to start the cycle anew.
The heating cycle is similar to the refrigeration cycle, but with the useful work being done at the opposite point of application. In an air-conditioning system, inhabitants receive cool air conditioning from the evaporator unit. However, in a heating system, inhabitants receive warm heat from the condenser. Heating units usually refer to the evaporator as the boiler and the condenser as the radiator.
The heat provided at the boiler is provided by applied heat energy generated by the burning of a fuel source (or by an electrical heating element) instead of by ambient heat from the surrounding air. The point of adding heat from a burning fuel source is to raise the temperature of the fluid much higher than adjacent air, so that it can heat rooms and buildings. For this reason, water has been the traditional heating fluid, flashed to high temperature steam in the boiler and carrying that heat to radiators, which then deliver the heat to cold living spaces to warm them up.
Ventilation is the third part of HVAC systems. Instead of exchanging heat for cold, it exchanges low-quality air for high-quality air. It removes air with low oxygen content, air with too much moisture, and air laden with impurities (smoke, airborne bacteria, cooking grease, dust, carbon dioxide, or odors). By constantly replenishing indoor air with fresh outside air, it keeps air circulating and prevents air from stagnating. In addition to bringing air in from the outside, a ventilation system circulates air from room to room inside a building. Mechanical ventilation uses fans and blowers to force air into circulation and extract it from outside the building. Natural ventilation takes advantage of warm air rising inside the building to create an updraft as the warm air escapes from vents in the roof. This updraft draws in cool outside air though vents in lower portions of the building. A ventilation system can be operated independently of heating and air-conditioning systems, with its own ductwork and vents, or it can be an integral part of these systems, providing air flows for the heating and cooling elements as it brings air into the building.
Overall system efficiency is determined by several rating numbers. “Seasonal Energy Efficiency Ratio” (SEER) is the average efficiency at which a central air conditioner will run under various climate conditions that occur between hot summer months and warm spring or fall months. A SEER rating of 13 is considered average for American systems, with a SEER of 16 indicating a highly efficient system. “Energy Efficiency Rating” (EER) is a more specialized rating that indicates how well an air conditioner will run at peak loads on hot days. EER values range from 8 to 15, with an EER rating over 12 considered excellent.
Smart HVAC Systems
The basic HVAC control system element is the thermostat. This simple mechanical device reacts to room temperature and provides feedback to an on/off control for the heating or air-conditioning system. But compared with more advanced system controls this results in relatively poor temperature management and increased expense over the lifetime of the system. When set at a particular temperature, the on/off action can result in an HVAC system swinging wildly as much as 10 degrees hotter or colder than the thermostat’s set point.
Recently developed smart controls for HVAC systems will cost more than a simple thermostat, but they have the potential to generate considerable savings over their operational lifetimes. Their ability to provide temperature variability allows for fewer on/off cycles and less variability in room temperatures. Using sensors that determine if a room is occupied or a portion of the building is receiving shade from an adjacent tree allows the system to adjust for individual room variables. In addition to sensors in each room and living space, sensors can be integral parts of the various system components themselves. A more consistent operation also results in better humidity control.
All in all, smart HVAC operates with less energy at significant cost savings with an extended operational lifetime for the systems themselves, even in extreme climates. Smart HVAC, therefore, results in both operational and capital cost savings. It can also result in an immediate 20% increase in energy efficiency (with corresponding reductions in operating costs).
What makes a smart HVAC system so “smart”? Sensors. Sensors located in individual rooms can determine everything from utilization rate, amount of body heat being generated by occupants, rate of airflow in and out of the room, etc. They can monitor the performance and adjust the operation of the various HVAC system components in real time. They can communicate with each other, balancing heating and cooling loads between different rooms. They can communicate with thermostats and Web-based software applications that track their performance and allow for remote monitoring. They can notify the building manager about broken components, leaking refrigerant, clogged ventilation filters, etc. All of these sensor, communication, and feedback operations result in better and more efficient control of temperature, air flow, humidity, pollen and dust, and heat and cold. As they do so, they calculate and factor in outside climate, the percent of the exterior walls made of glass, and the sizes of individual rooms. They provide greater comfort to the occupants as they provide greater cost savings to the owner.
Recent Advances in HVAC Efficiency
Control systems are not the only source of improvements in HVAC operational efficiency. Mechanical and transmission components have also been improved to operate more efficiently and cost less to install. The key word in HVAC technology advances is “efficiency.” The emphasis on green technologies has recently taken a back seat to overall cost effectiveness. But, in the long run, more efficient use of available resources is itself a green technology. And it is occurring through a series of incremental improvements, rather than major breakthroughs.
One example of recent improvements in the increased efficiency of chiller units. Current chillers offer peak load efficiencies 25% higher than just 10 years ago. Furthermore, in part due to the use of variable frequency drives, the seasonal load efficiencies for chillers have increased by more than 50%. Boiler systems show similar improvements, with recent boiler systems approaching 95% operational efficiencies.
Even something as simple and basic as standard maintenance has seen impressive improvements. New diagnostic tools ensure that HVAC systems run much longer at peak efficiencies with fewer breakdowns. These diagnostic software packages that extract performance data and analyze energy usage issues allow for a further 15% increase in operational efficiency.
A technology so advanced it’s simple: energy recovery wheels. There are heat wheels that deliver sensible heat, and enthalpy wheels that deliver both sensible and latent heat (humidity). An energy recovery wheel of either type is a device that is placed inside an air handling unit that has two airstreams. These airstreams are incoming outside air as defined by ASHRAE 62 ventilation requirements, and exhaust from the building as required for removal of space pollutants (volatile organic compounds) or building pressure relief. The purpose of the recovery wheel is rotate between the two airstreams, recovering the conditioned exhaust air, and using that energy to pretreat the incoming outdoor air prior to further outdoor air conditioning through mechanical means.
The wheel is typically made of aluminum, although some manufacturers use synthetic or fibrous materials. The aluminum itself is a conductor of heat and as the outdoor air passes through one half of the wheel, it heats the aluminum up. When that half of the wheel rotates into the exhaust side of the wheel, it cools the aluminum down. The converse happens in the winter when the wheel is recovering the exhausted heat to warm the outdoor air before being further mechanically heated. Temperature is only one part of the equation. The first energy wheels were commonly referred to as “heat wheels” because they only transferred temperature as described above. As the technology advanced, desiccant was added to act as a sponge to transfer humidity from one airstream to the other through vapor pressure. So in summer, the humid outdoors would be adsorbed onto the sponge and released into the dryer exhaust air. Likewise, the wintertime operation would recover the exhausted humidity from the space and transfer it to the dry winter outdoor air.
The energy and cost savings from well-designed wheels can be significant. As Explained by Tom Rice of SEMCO, “Wheels are not perpetual motion devices or 100% efficient. As with all energy savings methods, there is no free lunch and with wheels, the negative result of the process is additional fan energy due to increased static pressure. When manufacturers design wheels there are two common approaches: to design the wheel with a tight matrix design to increase the effective transfer, or to design the wheel with a balance of mass and pressure. It is important to understand that temperature transfer is based on how much wheel mass is in the wheel, and the amount of latent transfer is related to the amount of sponge material that resides on the wheel. When you strike the balance, you will find that the overall system efficiency will be improved because the penalty of fan energy is mitigated while providing a reasonable energy wheel recovery.”
AAON Products. You would think that a company that leads the industry in seismically certified HVAC units and components would be located in California, but AAON is based in Texas and Oklahoma. The term rugged survivability does not begin to describe their HVAC equipment that has been certified to remain operational even after seismic events.
This is especially important for buildings and facilities providing essential services in the event of an emergency or catastrophe, including: hospitals and emergency care centers, police and fire stations, communications centers, schools and community centers, government centers, data centers housing mainframe computers, and other critical facilities. It is not just a matter of creature comforts, maintaining climate control in these facilities is essential to their effective operation. AAON rooftop units are engineered with double-walled rigid polyurethane foam-insulated cabinet construction. They come equipped with direct drive backward curved plenum fans providing energy-efficient air flows with high static pressure capabilities. Their packaged DX series rooftop units range from 2 to 240 tons with electric, gas, hot water, steam heat, and/or air cooling capabilities. Non-compressorized DX units can be paired with matching condenser units, or chilled water handling units can be mated with existing cooling systems for additional capacity.
Hardware isn’t the only advanced AAON application. Their Single Zone Variable Air Volume (VAV) systems combine variable capacity compressors, variable speed fans, and optimized controls to save energy at all loading conditions. The supply fans modulate based on the space temperature, and the compressors modulate based on the supply air temperature. These systems also do not require a complicated VAV duct damper system to install and maintain. Advanced Makeup Air ventilation systems combine variable capacity compressors, variable speed fans, energy recovery wheels, modulating humidity control, and optimized controls to provide precise control and save energy during both occupied and unoccupied hours of operation. The supply fans and air-side economizer dampers modulate based on the ventilation requirements, from 100% outside air during fully occupied hours to 100% return air during unoccupied hours. The compressors modulate based on the supply air temperature. Modulating humidity control is used to provide dehumidification of the ventilation air without supply air temperature swings.
Coolerado. This company’s newly patented technology uses 50% to 90% less energy. A 13 SEER air conditioner can use up to 1,100 W per ton, while an equivalent Coolerado air conditioner uses just 600 W. Their new technology utilizes a unique indirect evaporative cooling technology without the need for chemical refrigerants and compressors. Instead, their system runs fresh outside air through air filters and then through a heat mass exchanger. Coolerado is different because their cooling technology is the proprietary and patented Maisotsenko Cycle. No one else in the industry uses this technology. Their air conditioners use air as energy for cooling; they get more efficient as the outside temperature rises, and use 100% fresh air and do not add humidity to the cooled air that goes into the space.
An innovative mechanical system is matched by an equally enlightened approach to the environment. This is shown by the system installed at the National Snow and Ice Data Center (NSIDC) in Boulder, CO. Ironically, the system the NSIDC was using was actually contributing to global warming. The energy needed to cool its data servers used over 50% of its total energy use, for only 2% of the building space. The systems upgrade utilized eight Coolerado M50 air conditioners installed inside the data center. The result was as much as a 97% reduction in energy use.
CES Group. CES has pioneered the practical application of fan arrays for HVAC systems with the development of FANWALL TECHNOLOGY by HUNTAIR, Inc. This innovative air-moving technology continues to set the standard for quiet, vibration-free operation, high efficiency at both minimum and maximum air flows, and low-cost maintenance and service. FANWALL TECHNLOGY features include custom fan wheel designs and inlet cones to maximize airflow efficiency, a robust cube design and silencing system to minimize sound and vibration, and control algorithms to optimize performance in variable airflow applications. Applications for FANWALL TECHNOLOGY range from office, education, and hospitality facilities, to facilities with critical requirements such as hospitals, data centers, and pharmaceutical manufacturing plants.
Thermax. Their Absorption Cooling utilizes lithium bromide Vapour Absorption Machines (VAMs) as a cost-effective alternative to electricity-driven compression chillers. VAMs can be powered by multiple heat sources (hot water and steam, natural gas and liquid fuels, hot exhaust gases, or some combination of all of these). VAMs that use ammonia as a refrigerant are available for sub-zero applications. VAMs can be customized for varied applications and temperature profiles ranging from 50°C (122°F) to 40°C (104°F).
Semco. Utilizing their enthalpy wheel technology, SEMCO provides their advanced Pinnacle PVS (Primary Ventilation System). The Pinnacle is comprised of a supply fan, exhaust fan, total energy wheel, cooling coil, and a passive dehumidification wheel. The total energy wheel is used to precondition fresh air using the exhausted building air. The cooling coil and passive dehumidification wheel then work in concert to further treat this fresh air stream to produce room temperature air at a much-reduced humidity level. The key to this system is the passive dehumidification wheel. It is optimized to remove moisture from a saturated air stream, without an active regeneration source. Pinnacle reduces energy consumption for cooling by as much as 49%. In winter, energy consumption for heating and humidification can be reduced by 89%.
Arctic Chiller Group. This company’s emphasis on energy efficiency has produced their Turbocor modular chiller units. These are modular chillers with redundant digital scrolls or magnetic-bearing oil-free Turbocor compressors and come equipped with pumps, free-cooling, VFD fans, valves, and optimization algorithms and leading edge controls. Their chillers include individual refrigerant circuiting with brazed plate sub-coolers to work across a much wider range of ambient temperatures. In the area of HVAC controls, Arctic Cool provides their Energy Optimization Controller (EOC). This is an energy-efficient chiller plant controller. It is operated by open-protocol hardware. This hardware runs in live-execution mode (faster than Windows embedded code). The system supports real time monitoring, staging and control of multiple chillers.
Honey/Emon. Honeywell’s latest innovation is not some new technical breakthrough. Rather, it is the simple concept of superior service. Their new Attune Advisory Services is a suite of professional services that combines cloud-based tools and analytics with a global network of operations centers and energy and facility experts to provide enhancements that can reduce utility bills and operating expenses up to 20%.
“The performance of building systems and equipment can degrade by as much as 5% every year, which translates to energy and operating costs that continually escalate,” says Paul Orzeske, president of Honeywell Building Solutions. “Companies are starting to realize the significant impact this can have, as well as the opportunity it presents for bottom-line savings. With Attune, we’re providing the ease and convenience of cloud-based technology with expert advice and actionable guidance so companies can capture and maintain those savings.”
Also making HVAC systems run more efficiently is their ComfortPoint Open Building Management System to control and optimize heating and cooling equipment in facilities. ComfortPoint improves ease of use through Web and mobile accessibility, reduces energy costs with built-in utility meter management tools and advanced energy reporting, and provides flexibility to grow and expand with end-to-end BACnet integration. An intuitive user interface allows operators to easily access data online, providing remote 24/7 control capabilities. Operators can also use the Honeywell EasyMobile client interface to manage and control equipment from a variety of mobile devices, such as a smartphone or Apple iPad. Overall, ComfortPoint allows for easy installation and integration with other facility systems (such as lighting, security, and life safety equipment) through Honeywell’s building automation platform, Enterprise Buildings Integrator (EBI). ComfortPoint Open can also connect with Honeywell Attune Advisory Services to support advanced building performance analysis, continuous commissioning, and building optimization to help maximize system uptime and reduce long-term costs.
Improvements in HVAC performance and efficiency are just beginning. The resulting cost savings are a big deal, not just to building operators, but also to the economy as a whole. In fact, according to the International Energy Agency (IEA), buildings account for nearly 40% of energy used in most countries, and the IEA says the potential for savings is significant and can often be achieved at low or no costs.
Smart HVAC controls and information systems combined with incremental improvements on operating component design and maintenance have yielded stunning cost savings compared to even 10 years ago. It’s the magic of compound interests (small improvements made over time) that have yielded these impressive results. Though this means further anonymity for HVAC systems as they perform better and go unnoticed, it is the kind of performance that can put you in the Hall of Fame.
Author’s Bio: Daniel P. Duffy, P.E., writes frequently on the topics of landfills and the environment.