Human Comfort And Thermal Comfort Executive Essay


The main reason for the HVAC system is to attain clean indoor quality of air and individual comfort (thermal comfort), there are extensive HVAC systems a creator or owner gets the option to select predicated on the factors including the type of the building, structures, location, shape, adjoining environment, occupancy, envelop, level and regularity of activities, and the machine operation routine.

In addition to the aforementioned base factors that an HVAC system is likely to be selected upon, the energy intake, system efficiency, first and operational cost, and finally, feasibility (brief and long term rebound positive result) are of the owners and designers critical concerns.

This newspaper will discuss the elements of a typical feasible high performance low priced, fine tuned HVAC DDC integrated system to attain the best for users, owners, and environment.

1. Introduction

HVAC and its associated auxiliaries system are major energy consumers in a building, the immediate development of the advanced technology nowadays improves the HVAC system feasibility as more technical control systems are developed for this industry and extra fine-tune, quick response, standardized communication, simple control and monitor, and remote accessibility.

The BMS/DDC (Building Management System/ Direct Digital Control) included system is the key of the good feasible high-efficient HVAC system.

The BMS is the most recent High-Tech energy management system that manage a building performance to the utmost desirable pre-determined set of parameters which in a position to control, keep an eye on, adjust, save and record mostly all the building facilities and resources when integrated challenging appropriate building's Sub-LANs, a DDC is one particular LANs and can talk to other control LANs under the guidance of the BMS.

BMS can supervise, control, change and record the illumination, electric power control, HVAC, security and observation, magnetic card and access, open fire alarm, lifts, and other executive systems.

Integrated with the BMS, the DDC performs the HVAC control management and communicates with the other building controllers via the BMS to attain integration predicated on a specified, programmed event collection.


The DDC is the heart of a competent HVAC system, it finely tunes the digital/analog type/output communication between receptors, probes, stand-alone controllers, LANs controllers, and finally the controlled factor that could be an actuator that adapt the process varying (flow, temps, level, or pressure), and permits a feedback transmission to further adjust the required process set-point. This entire process is reported in a real-time manner to the BMS system for even more coordination with the other building's controllable systems to attain integration based on the pre-programmed guidelines.

In order to achieve the highest individual comfort, energy conservation, and a permanent rebound effect strategy, The BMS/DDC system should be interlocked and integrated with a high-efficient and feasible HVAC system, this mixture can awards energy preservation, system and environment sustainability, individuals comfort, and business feasibility.

An Optimal Air System is a good example of a low-coast, high-performance, energy-efficient and a good investment for long-term rebound pay-back impact.

Optimal Air System theory is based on the low temp supply system that requires, less energy utilization by the most energy consumer auxiliary this is the fan, this affects the sizing of the ducts (less duck size), air handling units and lover motors, all of which will be smaller and ends in a system that will require less space and uses less vitality.

As this paper focuses on the HVAC/DDC built in system software for human being comfort, energy preservation, and feasibility (long-term rebound effect), I am going to discuss and focus on the DDC and Optimal Air System integration for the above purposes and define characteristics, elements, and functions of both systems.


2. DDC

DDC has became the latest and the most recently used system for HVAC control buttons after the pneumatic and electromechanical control systems, digital pre-programmable controllers are designed for extensive digital/analog data process from inputs (detectors, tranceducers and transmitters) that tyapically mesure heat range, flow, dampness, pressure or level, and outputs to last managed devices to adjust a process varying predicated on a preset guidelines, also recives a opinions alerts from inputs again to further adjust signal demand mistakes for best results based again on the setpoints. Digital inputs are Free of moisture connections from a control device, analog inputs are voltage and current signs that mesure variables such as humidity, pressure, level or circulation form sensing devices and converted to ratio. Digital outputs are of 1 1 or 0 binary that either prevents or starts gadgets with a relay, analog outputs are voltage or current alerts that control an activity adjustable control devices such as valves, motors or dampers. The DDC program code may be custom-made for designed use such as: Time routine, sequence of procedure, pattern logs, alarms.

2. 1 Elements of a DDC

As explained above, the three useful elements needed to perform the functions of an DDC system are

a) A way of measuring component (Sensor, prob, Transmitter, Transducer)

b) An error detection element (Digital/Analog/pneumatic Controller, PCU)

c) Your final control element (Motor/Piston Actuator, VFD, VSD, Relay)

2. 2 DDC controled mediums

The DDC manages two parameters

I. A controlled variable is the procedure adjustable that is looked after at a given value or inside a specified range.

II. A manipulated variable is the process that is acted on by the control system to maintain the managed variable at the specified value or within the given range.


2. 3 Functions of DDC system

In any DDC, the four basic functions that occur are

a) Measurement

b) Comparison

c) Computation

d) Correction

3. DDC LAN-WAN Configuration

DDC is where mechanised and electrical power systems and equipment are joined with microprocessors that talk to each other and to a central computer BMS. This computer and controllers in the building Management system can be networked to the internet or provide as a standalone system for the neighborhood peer-to-peer controller network only Fig 1. Also, the controllers themselves do not need a computer to operate efficiently as much of the controllers are designed to operate as stand-alone controllers and control the specific equipment they are simply assigned to control.

Fig 1. Typical peer-to-peer controller network [1]


With a few exceptions, each DDC or building automation controller supports their own programs and has the capacity to converse to other DDC building automation controllers. It is important for the DDC or building automation controllers to speak to each other. When the network fails for reasons uknown then your system may still function (because the DDC controllers in a BMS system are stand-alone) but you won't function as efficiently as designed.

The DDC/BMS system can be configured as self-employed (localized) closed-system, or DDC open-system predicated on availability options required by several buildings managed by a single company or property management firm (centralized), or an individual property to be monitored and managed by its own (localized) Fig 2.

Fig 2. DDC/BMS LAN/WAN configuration [2]


3. 1 BACnet compatibility

BACnet is the word frequently used to make reference to the ANSI/ASHRAE Standard 135- 1995, implemented and recognized by the North american National Criteria Institute (ANSI) and the American Society of Heating up Refrigeration and Air-Conditioning Technical engineers (ASHRAE). BACnet stands for Building Automation and Control network. BACnet is a true, non-proprietary open protocol communication standard conceived by the consortium of building management, system users and manufacturers [3].

A closed protocol is a proprietary process used by a particular equipment manufacturer. An open process system runs on the protocol available to anyone, however, not published by way of a standards organization. A standard protocol system uses a protocol available to anyone. It is created by a standards group.

Open Systems

An open system is thought as a system that allows components from different manufacturers to co-exist on the same network. These components

would not desire a gateway to communicate with each other and wouldn't normally require a producer specific workstation to imagine data. This might allow several vendor's product to meet a particular application need.

The DDC/BMS' BACnet based mostly LANs and Sub-LANs can be reached, controlled and supervised from remote locations via the Internet trough a centralized data management system which is capable of collecting data from multiple sites. That is accomplished by attaching with a gateway for collecting data from the lighting and air-conditioning control systems installed in each building or manufacturer, and the center server for providing data collection, database and web server functions along with security methods applied to all sent data.

Based on the capability of real-time monitoring and evaluation of real energy use such as electricity and gas from a distant location by by using a web browser, this system can achieve the maximum level of energy saving in buildings and factories which in turn, reduce the emissions and the environmental impacts by firmly taking good thing about its cost performance and by limiting the required energy for a particular application or function.


Fig 3, Integrated BACnet founded WEB Browser BMS Control System Layout [4]


4. DDC/BMS integrated features, application and functions

4. 1 Energy saving

DDC/BMS allows the owner to create schedules of procedure for the gear and light systems so that energy personal savings can be recognized when the building or spaces in the building are unoccupied.

Have algorithms as reset schedules for warming vegetation, static pressure control, and other systems where energy cost savings can be realized through these predictive programs.

4. 2 Individuals comfort (thermal Comfort)

DDC/BMS system allows the gear optimal focus on pre-scheduled program. Maximum start is allowing the gear to be brought on in an bought and sequential manner automatically on the schedule prior to the building is reoccupied so that space place items can be came to the realization before occupation. Event sequence coding features allow the system to compare space heat, outdoor air conditions, and equipment capacities so that the equipment can be fired up at a proper time for you to ensure space place points are achieved before profession.

Have cut and respond functions. Based on area demand the collection point for various cooling and heating sources will change according to demand from the zones. For example, in a Variable Air Volume system, all the VAV containers are served from a central air handling unit. If all the areas are at collection point then the supply air heat range place point of the environment handler is automatically evolved to prevent mechanised cooling from taking place when it's unnecessary. When the zones grow warmer the resource air temperature placed point is automatically reduced to allow mechanical cooling to satisfy demand.

In conjunction with the appropriate mechanised system set-up, offer economizing based on enthalpy calculations and/or CO2 set in place point control.

4. 3 Long-term rebound effects

Offer load shedding when electricity companies are in peak demand and need business and industry to cut-back on electricity usage to avoid dark outs. Building Management systems for illustration, permit the owner to pattern various things off like normal water heaters or drinking fountains where use of the things-


-will not be noticed even though they are simply off.

Management companies who acquire a good DDC/BMS can create the machine to expenses tenants for energy utilization (fewer employees required).

4. 4 Proactive

Ability to send alarms via email, pager, or mobile phone to warn building professionals and/or technicians of the developing problems, and system failures.

4. 5 Other applications and compatibilities

Have the capability to monitor energy usage including the ability to meter electric, gas, water, steam, hot water, cold water, and fuel oil services.

Have the communications skills to be included with other properties via WAN setup using the standardized TCP/IP category of protocols. It really is BACnet base web browser appropriate and other wide open source communication protocol which allows the machine to be seen via the net browser from remote locations. (Make reference to 4. 2)

5. High-performance Low-energy HVAC design

Recall the Benefits, In addition to BMS/DDC System program for energy saving and high HVAC system performance, a renewable HVAC system design will achieve all aspects of comfort, energy conservation, low primary and functional capital costs, and adds more efficient performance in conjunction with the DDC system, a good example of such inexperienced HVAC system would be an Optimal Air System [5].

Optimal Air System theory, idea and example are extracted from McQuay Air Conditionning/2002 McQuay International/Application Guide AG 31-005 for example to illustrate its benefits for energy preservation, human being comfort, lower preliminary cost and permanent rebound effects.

Optimal Air systems uses less energy than regular systems by using an annual basis, for example, In a conventional system, supply air temperature ranges run between 54F -57F from the environment handling product. With duct high temperature gain, the source air ranges from roughly 56F-59F from the air diffuser.


In Optimal Air System, resource air temp run between 45-52F from mid-air handling product to optimize energy use, reduce first capital cost and improve wetness control. Optimal Air has for years been extensively found in grocery stores and is also gaining increasing level of popularity in comfort cooling applications such as offices and schools.

5. 1 Advantages

There are several advantages of Optimal Air which make it a stylish system for use in a wide variety of applications.

It Saves Space and Reduces Energy and Construction Costs, escalates the amount of practical heat that all CFM delivered to a zone can absorb. While 50F air may not seem to be much colder than 55F air, the delta T increases from 20F to 25F. That's a rise of 25%.

This influences the sizing of the ducts, air controlling units and lover motors, all of which will be smaller and ends up with a system that requires less space and uses less electric power. In many applications, fans can use more power yearly than refrigeration (chillers, condensing devices, pumps, and compressors).

An example of annual 10-report building energy utilization of 200, 000 square-feet of HVAC components, the supporter energy use is high because the supporters operate every hour the building is occupied providing minimum air movement, ventilation air, heating system, etc. In this case, an Optimal Air system could have an extremely real impact on overall energy costs.

Fig 4, Total annual HVAC Energy Use [6]


5. 2 Less Humidity, more comfort

Optimal Air systems take more moisture out of the return and ventilation air blend as it moves over the cooling down coil. The lower moisture content in the source air reduces the "Psychrometric balance point" dampness level in the conditioned space. This allows the space temperatures to be arranged higher while attaining the same comfort level for occupants and further reduces the source air variety and fan electric power requirement.

5. 3 Quieter and Improve Indoor Air Quality (IAQ)

The lower air quantity necessary for Optimal Air systems makes them quieter than classic systems. Fan audio technology is a function of enthusiast type, static pressure and air amount. By minimizing air quantity (and frequently the total lover static pressure) Optimal Air systems create lower fan sound which can cause more suitable space conditions. This reduced sound generation can also be used to reduce the expense of any required noises attenuation in critical applications.

The lower required air volume can even be used to lessen filter face velocities, allowing better filters to be used without high energy cost fines. The lower air heat range and resultant wetness levels also reduce the chance of mildew expansion in the air handling systems, ducts or the occupied space.

The exemplory case of the building above requires a supply air of 26, 667 CFM. The HVAC system is floor by floor VAV air controlling products with a two chiller major supplementary system, Optimal air works similarly well with applied rooftop systems or inside vertical self-contained systems.

Table 1, HVAC system performance with best air system [7]


Table 1 shows the HVAC system performance as the resource air heat, to the duct, is decreased. It is important to differentiate between resource air temperature from the cooling coil and offer air temperature into the duct.

To accommodate the low supply air temps, the chilled water supply heat (CWST) was gradually lowered, the environment handling device coils deepened to allow for closer methods, and chiller performance was tweaked to offer will the increased lift up. For their basic operating differences, DX rooftop and self-contained systems may have some other Optimal Air heat than a chilled water system. When contemplating multiple system options, it's important to use Energy Analyzer for every single in order to identify your best option.

5. 4 Optimal Air Balance Point

Reduced supporter energy must be "traded off" against increased refrigeration energy. This trade off varies with the kind of building, the sort temp control system, the sort air-con system and geographic locale. Therefore, the "optimal" source air temperature differs for every job. When only energy costs are one factor and no thermal storage is engaged, this optimal supply air temperature generally comes in the 47F -52F range. It could be determined by comparing total system energy use with varying source air temperature ranges using a power evaluation program.

5. 5 Space Design Temperatures and Related Comfort

Temperature, humidity, air speed and mean radiant heat directly affect occupant comfort. Standard designs are usually based on keeping 75F and 50% RH (Relative Wetness) in the occupied space. Physique 5 shows the ASHRAE comfort zone where 80% of individuals involved in light office work are satisfied. As the relative humidity is lowered, the space air temps can be increased and still provide occupant comfort.

The departing air condition from the air handling unit is the generally control of the relative dampness in the occupied space.

The internal moisture content profits from people, kitchens, etc, as well as infiltration also play a part.


Fig 5, Equivalent comfort chart [8]

In most climates, the lower the resource air temperature, the low the humidity ratio and the drier the area. Amount 5 shows reasonable heat percentage lines for regular, Optimal and low resource air temps. As the space relative dampness is lowered, the space temperature set-point rises from 74F to 78F.

5. 6 ASHRAE Compliance

The 1999 and 2001 version of ASHRAE Standard 90. 1, Energy Standard for Structures except Low Climb Residential Buildings [9], has compulsory requirements for refrigeration equipment and prescriptive requirements for lover work. The Standard identifies that Optimal Air systems improve lover work significantly and credits to account for improved fan performance. In addition, refrigeration system performance is ranked at typical conditions or special desks are given to account for non-standard operating conditions (as is the truth with centrifugal chillers). In any case, ASHRAE Standard 90. 1 does not penalize Optimal Air systems.


5. 7 Design Considerations

Design of refrigeration and air handling equipment for an Optimal Air system is similar to the design of a typical air temp system. Attention must be paid, however, to air syndication, control buttons and duct design. Standard diffusers, when properly applied, will continue to work with Optimal Air.

Controls also require only modest changes from regular systems. Specifically, programming of economizer settings and offer air temps reset. Finally, the ducting system must be size for the reduced air level to use full good thing about the potential capital savings. Duct insulation and sweating also needs to be reviewed to give a trouble free system.

Not every building type is an excellent applicant for Optimal Air. When air volumes are dictated by air turnover rates, such as some healthcare applications, Optimal Air offers no advantages. In fact, there would be increased reheat costs. Office buildings are a solid applicant for Optimal Air. They have got high sensible temperature ratios and typically significantly less than 20% ventilation loads. Schools can be a possibility. Generally speaking, as the ratio ventilation load increases, Optimal Air becomes less attractive.

Location and climate also impact if Optimal Air is an excellent prospect. Locations where weather provides significant economizer time between 45 and 55F will limit the savings. Ultimately, each task must be examined by doing the suitable specific calculations. The next should be considered

Load and Balance Point computations, Space Temperatures Set-point analysis, Design Load Computation, Primary and Extra System Selection, Parallel, blending or series VAV-Fan driven boxes, Perimeter Home heating, Air Syndication, Diffusers (based on ventilation and the chuck distance calculation), Duct design (considering duct heat gain, perspiration and insulation).

5. 8 System Life-Cycle Analysis

Evaluating different engineering solutions is actually part of a good proposal. Optimal Air systems are no different.


In the case of Optimal Air, there could be you don't need to do any calculations because Optimal Air systems cost less to develop (lower capital cost) and have the same operating cost as regular systems (presuming the balance point was used for the design).

Duct sizing will decrease almost linearly with reduction in air quantity. The installed cost won't change linearly because of the labor part. A 20% reduction in air level can result in 80% savings of the 20% reduction or 16% overall savings in sheet metal cost.

On the plus part, there are less pounds of material and fewer man-hours to set up it. In the minus side you can find more insulation. Terminal boxes and diffusers is a wash since there are fewer of these but the equipment cost will be higher than standard equipment.

HVAC equipment will cost about the same. This is conventional because mid-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 ought to be the same for new structure. Regarding retrofit applications, it will depend on the grade of the prevailing building.

The cost of space could also need to be examined. Not accounting for space savings is conservative. You will see space savings nevertheless they may be difficult to realize. If enough plenum elevation cost savings can be became aware to include another floor within the same building envelope, then that rentable space should be accounted for.

Simple payback calculations do not consider the price of money, taxes and depreciation, inflation, maintenance or heightens in the price of energy. A more complete analysis will include Internal Rate of Come back (IRR) and online present value (NPV). In the HVAC industry, many tasks fail simple again (they may be in the 5-year range) while moving IRR (they give you a 25% rate of come back).

Software examination tools can be used to perform both energy and life-cycle examination that include simple payback, IRR and NPV.


6. Conclusion

Building owners and designers confronted with increased concerns for energy saving and environmental stewardship seek out affordable system options for their projects.

The DDC, integrated with a high-performance low-energy HVAC system as the perfect Air system can deliver both low first costs and reduced energy costs in a fresh building and retrofit applications. This built-in system can not only meet the efficiency and sustainability of its performance at the desired set-parameters, however when made with advanced selection tools, installed with the most advanced DDC/BMS system, and recognized by trained operators, will achieve both energy saving and long-term rebound impact (pay-back), maximum individual thermal comfort, in addition, it allows building owners to compare expected energy use to actual performance, this leads to a adaptable budgeting, further future system adjustment and energy utilization cut-back. The complete included DDC/BMS HVAC system function will also add in environmentally friendly impacts decrease.

In today's challenging energy efficiency, building owners need proven system that gives the necessary performance to meet their integrated environmental sustainability and business goals [10].

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