Human Comfort And Thermal Comfort Engineering Essay

Human Comfort And caloric Comfort Engineering EssayAbstractThe main purpose of the HVAC dust is to hand clean indoor style quality and gentlemans gentleman puff (thermal sympathiser), there ar m whatsoever HVAC arrangings a jut outer or possessor has the option to select lowd on the constituents much(prenominal) as the suit of the create, architecture, location, shape, surrounding climate, occupancy, envelop, train and frequency of activities, and the outline physical process schedule.In admission to the above base factors that an HVAC strategy is expected to be selected upon, the capability role, corpse efficiency, initial and in ope balancen(p) speak to, and netly, feasibility (short and dogged term rebound everyplacebearing put together) ar of the ingesters and designers critical concerns.This paper bequeath discuss the elements of a distinctive feasible towering execution low embody, fine tuned HVAC DDC integrate frame to achieve the bes t for implementrs, owners, and environment.1. Intro distribution channelionHVAC and its associated auxiliaries agreement of rules of rules are major verve consumers in a building, the rapid development of the groundbreaking technology like a s gamey boosts the HVAC system feasibility as more complex entertain systems are developed for this industry and obligeitional fine-tune, prompt response, standardized conference, ease of run across and monitor, and remote accessibility.The BMS/DDC (Building Management transcription/ Direct Digital Control) co-ordinated system is the core of a dependable feasible high-efficient HVAC system.The BMS is the most recent advanced cleverness management system that manage a building dressance to the maximum desir up to(p) pre-determined designate of parameters which able to soften, monitor, adjust, save and record mostly all of the building facilities and utilities when integrated with all of the compatible buildings Sub-LANs, a D DC is wizard of those LANs and squirt slide by with some other(prenominal) control LANs under the supervision of the BMS.BMS is able to supervise, control, adjust and record the illumination, electric power control, HVAC, security and observation, magnetic throwaway and access, fire alarm, lifts, and other engineering systems. integrated with the BMS, the DDC performs the HVAC control management and communicates with the other building controllers via the BMS to achieve integration ground on a specified, programmed emergence sequence.IThe DDC is the heart of an efficient HVAC system, it finely tunes the digital/analog enter/output communication between sensors, probes, stand-alone controllers, LANs controllers, and finally the controlled element which could be an actuator that adjust the process inconstant (flow, temperature, level, or pressure), and ceases for a feedback sign up to advertize adjust the desired process set-point. This whole process is reported in a rea l-time manner to the BMS system for further coordination with the other buildings controllable systems to achieve integration based on the pre-programmed parameters.In frame to achieve the highest human comfort, animation saving, and a long term rebound effect strategy, The BMS/DDC system should be interlocked and integrated with a high-efficient and feasible HVAC system, this combination washbowl awards talent saving, system and environment sustainability, human comfort, and business feasibility.An best activate system of rules is a good utilization of a low-coast, superior, animation-efficient and a good investment for long-term rebound pay-back effect. optimal oxygenate System sentiment is based on the low temperature come forth system that exacts, less readiness consumption by the most vital force consumer auxiliary that is the fan, this affects the size of the ducts (less submerge size), transmit treatment whole of measurements and fan motors, all of which volition be littler and upshots in a system that requires less position and uses less power.As this paper focuses on the HVAC/DDC integrated system finish for human comfort, energy saving, and feasibility (long-term rebound effect), I will discuss and focus on the DDC and best melodic line System integration for the above purposes and define characteristics, elements, and functions of some(prenominal) systems.II2. DDCDDC has became the latest and the most recently employ system for HVAC controls aft(prenominal) the pneumatic and electro mechanic control systems, digital pre-programmable controllers shag handle panoptic digital/analog information process from inputs (sensors, tranceducers and transmitters) that tyapically mesure temperature, flow, humidness, pressure or level, and outputs to final controlled devices to adjust a process variable based on a preset parameters, withal recives a feedback signals from inputs again to further adjust signal command breaks for b est issuings based again on the setpoints. Digital inputs are Dry contacts from a control device, analog inputs are potential and occurrent signals that mesure variables such as humidity, pressure, level or flow form spying devices and converted to percentage. Digital outputs are of 1 or 0 binary program that either stops or starts equipments via a relay, analog outputs are voltage or current signals that control a process variable control devices such as valves, motors or dampers. The DDC program code may be customized for intended use such as Time schedule, sequence of operation, twist logs, alarms.2.1 Elements of a DDCAs described above, the three functional elements exigencyed to perform the functions of a DDC system area) A measurement element (Sensor, prob, Transmitter, Transducer)b) An error detection element (Digital/Analog/pneumatic Controller, PCU)c) A final control element (Motor/Piston Actuator, VFD, VSD, Relay)2.2 DDC controled mediumsThe DDC controls two variabl esI. A controlled variable is the process variable that is maintained at a specified protect or inside a specified range.II. A manipulated variable is the process that is acted on by the control system to maintain the controlled variable at the specified value or within the specified range.12.3 Functions of DDC systemIn some(prenominal) DDC, the four basic functions that occur area) Measurementb) Comparisonc) calculationd) Correction3. DDC LAN- brainsick ConfigurationDDC is where mechanical and electrical systems and equipment are joined with microprocessors that communicate with each other and to a central computer BMS. This computer and controllers in the building Management system prat be networked to the internet or serve as a stand alone system for the local peer-to-peer controller network only Fig 1. Additionally, the controllers themselves do not requirement a computer to operate efficiently as many of these controllers are designed to operate as stand-alone controllers and control the specific equipment they are assigned to control.Fig 1. Typical peer-to-peer controller network 12With a few exceptions, each DDC or building automation controller holds their own programs and has the ability to communicate to other DDC building automation controllers. It is important for the DDC or building automation controllers to communicate to each other. If the network fails for whatever yard then the system may thus far function (because the DDC controllers in a BMS system are stand-alone) but it will not function as efficiently as designed.The DDC/BMS system can be configured as independent (localized) closed-system, or DDC open-system based on accessibility options demand by a group of buildings managed by a single company or glumice management firm (centralized), or a single property to be monitored and controlled by its own (localized) Fig 2.Fig 2. DDC/BMS LAN/WAN configuration 233.1 BACnet compatibilityBACnet is the term commonly used to refer to the ANSI/ASHRAE standardised 135- 1995, adopted and supported by the American National Standards Institute (ANSI) and the American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE). BACnet stands for Building Automation and Control network. BACnet is a true, non- patented open communications protocol communication standard conceived by a mob of building management, system users and manufacturers 3.A closed protocol is a proprietary protocol used by a specific equipment manufacturer. An open protocol system uses a protocol available to anyone, but not publish by a standards organization. A standard protocol system uses a protocol available to anyone. It is created by a standards organization.Open SystemsAn open system is defined as a system that relinquishs components from different manufacturers to co-exist on the homogeneous network. These componentswould not need a gateway to communicate with one another and would not require a manufacturer specific works tation to visualize info. This would impart more than one vendors product to meet a specific application requirement.The DDC/BMS BACnet based LANs and Sub-LANs can be accessed, controlled and monitored from remote locations via the Internet trough a centralized data management system which is capable of collecting data from multiple sites. This is accomplished by connecting with a gateway for collecting data from the lighting and aura travel-conditioning control systems installed in each building or factory, and the pertain server for providing data collection, database and web server functions along with security measures utilise to all transmitted data.Based on the capability of real-time observe and analysis of tangible energy consumption such as electrical energy and gas from a remote location by using a web browser, this system is able to achieve the maximum level of energy saving in buildings and factories which in turn, suppress the emissions and the environmental f urbish ups by victorious advantage of its cost effectiveness and by limiting the call for energy for a specific application or function.4Fig 3, Integrated BACnet based WEB Browser BMS Control System Layout 454. DDC/BMS integrated features, application and functions4.1 Energy savingDDC/BMS allows the owner to set up schedules of operation for the equipment and lighting systems so that energy nest egg can be realised when the building or spaces in the building are un diligent. expect algorithms as reset schedules for heating plants, static pressure control, and other systems where energy savings can be realized through these predictive programs.4.2 Human comfort (thermal Comfort)DDC/BMS system allows the equipment optimal start with pre-scheduled program. Optimal start is allowing the equipment to be brought on in an ordered and sequential manner automatically on a schedule before the building is re booked so that space set points can be realized before occupation. Event sequence programming features allow the system to compare space temperature, outside behavior conditions, and equipment capabilities so that the equipment can be turned on at an appropriate time to check glowering space set points are achieved before occupation.Have trim and suffice capabilities. Based on zone demand the set point for several(a) heating and cooling sources will change according to demand from the zones. For instance, in a Variable Air Volume system, all the VAV boxes are served from a central line of merchandise use unit. If all the zones are at set point then the cede railway line temperature set point of the air handler is automatically changed to prevent mechanical cooling from occurring when it is unnecessary. When the zones grow tepid the translate air temperature set point is automatically lowered to allow mechanical cooling to satisfy demand.In conjunction with the appropriate mechanical system set-up, offer economizing based on enthalpy calculations and/or carbon dioxide set point control.4.3 Long-term rebound effectsOffer gist shedding when power companies are at peak demand and need business and industry to cut-back on power usage to prevent pitch-black outs. Building Management systems for instance, allow the owner to cycle various things off like water heaters or drinking fountains where use of these things-6-will not be noticed even though they are off.Management companies who sustain a good DDC/BMS can set up the system to account statement tenants for energy usage (fewer employees required).4.4 ProactiveAbility to send alarms via email, pager, or shout to alert building managers and/or technicians of the developing problems, and system failures.4.5 Other applications and compatibilitiesHave the ability to monitor energy usage including the ability to meter electric, gas, water, steam, hot water, chilled water, and fuel oil services.Have the communications abilities to be integrated with other buildings via WAN setup usin g the standardized TCP/IP family of protocols. It is BACnet base web browser compatible and other open source communication protocol which allows the system to be accessed via the web browser from remote locations. (Refer to 4.2)5. high-performance Low-energy HVAC designRecall the Introduction, In addition to BMS/DDC System application for energy saving and high HVAC system performance, a green HVAC system design will achieve all aspects of comfort, energy saving, low initial and operational swell be, and adds more efficient performance in conjunction with the DDC system, an lesson of such green HVAC system would be an Optimal Air System 5.Optimal Air System concept, idea and object lesson are interpreted from McQuay Air Conditionning/2002 McQuay International/Application Guide AG 31-005 as an example to illustrate its benefits for energy saving, human comfort, lower initial cost and long term rebound effects.Optimal Air systems uses less energy than established systems on an an nual basis, for example, In a accomplished system, generate air temperatures run between 54F -57F from the air intervention unit. With duct heat gain, the supply air ranges from approximately 56F-59F out of the air diffuser.7In Optimal Air System, supply air temperature run between 45-52F from the air intervention unit to optimize energy consumption, reduce first capital cost and mitigate humidity control. Optimal Air has for years been extensively used in grocery stores and is gaining increasing popularity in comfort cooling applications such as offices and schools.5.1 AdvantagesThere are several benefits of Optimal Air that make it an winning system for use in a wide variety of applications.It Saves plaza and Reduces Energy and Construction Costs, increases the amount of advised heat that each CFM ram homeed to a zone can absorb. While 50F air may not seem much colder than 55F air, the delta T rises from 20F to 25F. That is an increase of 25%.This affects the sizing of th e ducts, air manipulation units and fan motors, all of which will be smaller and results in a system that requires less space and uses less power. In many applications, fans can use more power annually than infrigidation (chillers, condensing units, pumps, and compressors).An example of annual 10-story building energy usage of 200,000 square-feet of HVAC components, the fan energy use is high because the fans operate every hour the building is occupied providing marginal air movement, ventilation air, heating, etc. In this case, an Optimal Air system would have a very real impact on general energy costs.Fig 4, Annual HVAC Energy Usage 685.2 less(prenominal) Humidity, more comfortOptimal Air systems regard more wet out of the return and ventilation air mixture as it passes over the cooling coil. The lower moisture content in the supply air reduces the Psychrometric balance point humidity level in the conditioned space. This allows the space temperature to be set higher while ach ieving the same comfort level for occupants and further reduces the supply air quantity and fan power requirement.5.3 Quieter and better Indoor Air Quality (IAQ)The lower air volume required for Optimal Air systems makes them quieter than conventional systems. Fan sound times is a function of fan type, static pressure and air volume. By reducing air volume (and often the total fan static pressure) Optimal Air systems generate lower fan sound which can result in more desirable space conditions. This reduced sound generation can in like manner be used to reduce the cost of any required noise attenuation in critical applications.The lower required air volume can to a fault be used to reduce filter face velocities, allowing more efficient filters to be used without high energy cost penalties. The lower air temperature and resultant humidity levels in addition reduce the chance of mold growth in the air handling units, ducts or the occupied space.The example of the building above re quires a supply air of 26,667 CFM. The HVAC system is floor by floor VAV air handling units with a two chiller primary secondary system, Optimal air works equally well with applied rooftop units or indoor straight self-contained units.Table 1, HVAC system performance with optimal air system 79Table 1 shows the HVAC system performance as the supply air temperature, to the duct, is lowered. It is important to differentiate between supply air temperature off the cooling coil and supply air temperature into the duct.To accommodate the lower supply air temperature, the chilled water supply temperature (CWST) was gradually lowered, the air handling unit coils deepened to allow for closer approaches, and chiller performance was adjusted to deal will the increased lift. Because of their basic operating differences, DX rooftop and self-contained systems may have a different Optimal Air temperature than a chilled water system. When considering multiple system options, it is important to use Energy Analyzer for each in order to identify the best option.5.4 Optimal Air correspondence Point decreased fan energy must be traded off against increased infrigidation energy. This trade off varies with the type of building, the type temperature control system, the type air conditioning system and geographic locale. Therefore, the optimal supply air temperature is different for every job. When only energy costs are a factor and no thermal storage is involved, this optimal supply air temperature broadly speaking falls in the 47F -52F range. It can be determined by comparing total system energy consumption with varying supply air temperatures using an energy analysis program.5.5 blank Design Temperature and Related ComfortTemperature, humidity, air velocity and mean radiant temperature directly influence occupant comfort. Conventional designs are usually based on maintaining 75F and 50% RH (Relative Humidity) in the occupied space. Figure 5 shows the ASHRAE comfort zone where 8 0% of the people occupied in light office work are satisfied. As the congenator humidity is lowered, the space air temperature can be raised and still provide occupant comfort.The leaving air condition from the air handling unit is the primarily control of the congener humidity in the occupied space.The internal moisture gains from people, kitchens, etc, as well as infiltration also play a part.10Fig 5, Equivalent comfort chart 8In most climates, the lower the supply air temperature, the lower the humidity ratio and the drier the space. Figure 5 shows sensible heat ratio lines for conventional, Optimal and low supply air temperatures. As the space relative humidity is lowered, the space temperature set-point rises from 74F to 78F.5.6 ASHRAE ComplianceThe 1999 and 2001 edition of ASHRAE Standard 90.1, Energy Standard for Buildings except Low Rise residential Buildings 9, has mandatory requirements for refrigeration equipment and prescriptive requirements for fan work. The Standard recognizes that Optimal Air systems improve fan work significantly and provides credits to account for better fan performance. In addition, refrigeration system performance is rated at conventional conditions or special tables are provided to account for non-standard operating conditions (as is the case with motor(a) chillers). In either case, ASHRAE Standard 90.1 does not penalize Optimal Air systems.115.7 Design ConsiderationsDesign of refrigeration and air handling equipment for an Optimal Air system is similar to the design of a conventional air temperature system. Attention must be paid, however, to air distribution, controls and duct design. Conventional diffusers, when in good order applied, will work with Optimal Air.Controls also require only lowly changes from conventional systems. In particular, programming of economizer controls and supply air temperature reset. Finally, the ducting system must be sized for the reduced air volume to take full advantage of the potential capital savings. Duct insulation and perspiration should also be reviewed to provide a trouble free system. non every building type is a good candidate for Optimal Air. When air volumes are dictated by air turnover rates, such as some health care applications, Optimal Air offers no advantage. In fact, there would be increased reheat costs. Office buildings are a strong candidate for Optimal Air. They have high sensible heat ratios and typically less than 20% ventilation appoints. Schools can also be a possibility. Generally speaking, as the percentage ventilation load increases, Optimal Air becomes less attractive.Location and climate also impact whether or not Optimal Air is a good candidate. Locations where defy provides significant economizer hours between 45 and 55F will limit the savings. Ultimately, each project must be checked by performing the applicable specific calculations. The following should be consideredLoad and Balance Point calculations, Space Temperature Set-po int evaluation, Design Load Calculation, Primary and Secondary System Selection, Parallel, mixing or series VAV-Fan powered boxes, Perimeter Heating, Air Distribution, Diffusers (based on air flow and the throw distance calculation), Duct design (considering duct heat gain, sweating and insulation).5.8 System Life-Cycle AnalysisEvaluating different engineering solutions is always part of a good proposal. Optimal Air systems are no different.12In the case of Optimal Air, there may be no need to do any calculations because Optimal Air systems cost less to build (lower capital cost) and have the same operating cost as conventional systems (assuming the balance point was used for the design).Duct sizing will decrease almost linearly with reduction in air volume. The installed cost will not change linearly because of the labor portion. A 20% reduction in air volume can result in 80% savings of the 20% reduction or 16% overall savings in sheet metal cost.On the positively charged side, there are less pounds of steel and fewer man-hours to install it. On the minus side there is more insulation. Terminal boxes and diffusers will be a wash since there are fewer of them but the equipment cost will be higher than conventional equipment.HVAC equipment will cost somewhat the same. This is conservative because the air handling equipment will cost less and refrigeration equipment will be slightly more. There is typically more capital invested in air handling than refrigeration.Building envelope should be the same for new construction. In the case of retrofit applications, it will depend on the quality of the existing building.The cost of space may also need to be evaluated. Not accounting for space savings is conservative. There will be space savings but they may be onerous to realize. If enough plenum height savings can be realized to add another floor within the same building envelope, then that rentable space should be accounted for.Simple payback calculations do not take into account the cost of money, taxes and depreciation, inflation, maintenance or increases in the cost of energy. A more complete analysis should include Internal Rate of remember (IRR) and net present value (NPV). In the HVAC industry, many projects fail easy back (they are in the 5-year range) while passing IRR (they offer a 25% rate of return).Software analysis tools can be used to perform both energy and life-cycle analysis that include simple payback, IRR and NPV.136. ConclusionBuilding owners and designers faced with increased concerns for energy saving and environmental stewardship search for cost effective system options for their projects.The DDC, integrated with a high-performance low-energy HVAC system as the Optimal Air system can deliver both low first costs and reduced energy costs in a new construction and retrofit applications. This integrated system will not only meet the efficiency and sustainability of its performance at the desired set-parameters, but whe n designed with advanced selection tools, installed with the most advanced DDC/BMS system, and supported by trained operators, will achieve both energy saving and long term rebound effect (pay-back), maximum human thermal comfort, in addition, it allows building owners to compare predicted energy use to actual performance, this leads to a flexible budgeting, further future system adjustment and energy consumption cut-back. The whole integrated DDC/BMS HVAC system function will also contribute in the environmental impacts reduction.In todays challenging energy efficiency, building owners need proven system that delivers the necessary performance to meet their integrated environmental sustainability and business goals 10.