ASHRAE JOURN SUPP JUNE-1998 ASHRAE Journal (Supplement June 1998).pdf

1、 STD-ASHRAE JOURN SUPP JUNE L978-ENGL 1998 I0759650 0535b77 183 I HOW WE HELPED ONE SCHOOL DISTRICT PASS ECONOMICS A Study In Savings. Concerned with the poor air quality and high humidity levels in class- rooins, high school officials in Okeechobec, Florida, turned to Carrier for an afforciable sol

2、ution. Carrier designed and installed a customized rooftop system- and thc results were instanta- neous. The ncw system ran less often than its predecessor and used less energy. The school is now saving enough in energy costs, duc to higher efficiency lcvcls, that thc upgrade will pay for itself in

3、a few short years. Temperature And Humidity Control Earn High Marks For Comfort. The effects of the new Carrier system were inore than just economic. The MoistureMiser” dehumidi- fication package included in the new system eliminated inany serious building and equipment maintenance problems. And cla

4、ssrooms became much better learning environments, allowing students and teachers to be cornfortablc and more focused. According to Dale Rarrett of Okeechobee County Schools, “The new air conditioning system is exceeding expectations, and our Carrier contractor is right here in the county. Thats what

5、 were looking for-we have the system, service and Carrier name all in one package.” For inore information, or to obtain a copy of the full case study, con- tact your Carrier representative or call 1-800-CARRiER. www.carnier. com/edu 0 canfar au-i- MNER CORPOWLIION ISAIVIIOLLY OWNED SUBSIDIWY OF UNIE

6、OTECHNOLOOEF MRWRATION 91998 MRIER CORPOR4TION (Circle No. 1 on Reader Service Card) School Wasnt You dont need a large earthquake to do this kind of damage. Mild earthquakes as small L, l as Mercalli Intensity Level IV traditionally cause equipment, piping and eiectrical system failures. Over 80% o

7、f the USA is capable of seeing a seismic event powerful enough to knock out a schools HVAC and electrical system. This would turn the survivinq structure from a functioning school building into little more than a cave. Our kids desrve better. Mason Industries seismic snubbing systems, when properly

8、applied, will prevent system damage and allow the buildings mechanical and electrical elements to remain safe and functional. We are the recognized world-wide leader in earthquake protection for mechanical and electrical systems, piping and ducts. Mason Industries has been providing snubbing systems

9、 with proven track records for the past 27 years. Our professional engineering staff is happy to work with architects, engineers, contractors and school officials. Contact LIS for FKEE detailed information on Mason Industries seismic seminars, application engineering data and non-proprietary suggest

10、ed seismic specifications. Mason Industries shock and vibration control systems can ensure that our kids will have the proper learning environment to succeed. MASON INDUSTRIES, INC Manufacturers of NoIse 6. Vibration Control Products 350 Rabro Drive I HaLppauge, NY 1 1 788 Tel 51 6-348-0282 I FAX 51

11、 6-348-0279 E-mail Address Info Mason-lnd com Web Site http./www Mason-lndcom (Circle No. 4 on Reader Service Card) STD-ASHRAE JOURN SUPP JUNE L778-ENGL 1998 E U75b50 0535b77 T5b i ASHRAE JOURN SUPP JUNE L8-ENGL 1998 0757b50 0535b817 778 11 the facts about Standard 62-19239 can r air quality is a co

12、mplex issue with potential risks to below 60 percent to control mold and mildew growth. But maintaining humidity levels below 60 percent on part-load days can be difficult. fiats why Trane offers a variety of humidity management strategies including active humidity control for terminal units and ded

13、icated outdoor air dehumidification options for central humidity control. it is prudent to fully comply with all aspects of ndard 62-1989, which involves more than just cfm of ventilation air per person. Proper attention to source control, ventilation, humidity management on are all essential for ac

14、ceptable indoor air quality and Filtration Without a proper filtration system, airborne particles can circulate through the air distribution system, supplying a food their inherent design, WAC systems become an ideal environment for microbial proper source control, mold and mildew r wet surfaces and

15、 circulate through a result. ASHRAE 62 requires source for microbial growth and contaminating the entire building. ASHRAE Standard 62-1989 requires appropriate filtration levels to prevent building contamination. Trane offers a large selection of filtration options to meet these requirements. contro

16、l features on all air handling Trane is the solution ing drain pans that drain, cleanable s and easy access for cleaning. These ASHKAE Standard 62-1989 establishes the standard of care for WAC system designers. Trane makes it easy to provide acceptable indoor air quality the smallest fan coil unit t

17、o the largest central through a wide variety of products and systems without compromising ASHKAE 62 requirements. Our experience with indoor comfort systems spans over 80 years. Trane is the leading JAQ solutions provider and is qualified to help Ventilation Standard 62-1989 lists detailed ventilati

18、on requirements. ating VAVsystems to comply with these specitcations enging due to widely varying zone and system level reliable way to meet this challenge is to provide direct easurement and control at each VAV air handling TraqT“ system. This advanced system provides ation control and uses less fl

19、oor space than copy of this guide, contact Trane today. Learn the wztk Trunes Guzde to Undentandmg ASHRAE Stundurd 62-1 989 flow measurement methods. Call (608) 787-3990. E-mail us at . Visit our Web site at or contact your Trane commercial sales office. or relative humidity levels you fully comply

20、 with this standard. Learn the facts on compliance with Tranes Guide to U$tderstunding ASHRAE Standard 62-1989. To get a 1997 Creatipzg The Right Atmosphere“ (Circle No. 5 on Reader Service Card) The First Nume in 100% Fresh Air Cooling . Now With Gas or Electric Heat and Desiccant Wheels Both Air S

21、ource and Water Source! Ca ADDISON PRODUCTS COMPANY Quality Since 1949. 7050 Overland Road Orlando, FL 3281 O www.addison- E-Mail admin addison- Call today for info! (407) 292-4400 FAX (407) 290-1 329 (Circle NO. 6 on Reader Service Card) - STD-ASHRAE JOURN SUPP JUNE 179A-ENGL 1798 WO757650 0535b82

22、540 Practical Guide to HVAC for Schools 12 System Selection By Arthur E Wheeler, P E , Fellow ASHRAE 17 Special Systems By M. James Karpinski, PE, Member ASHRAE 22 Engineers, IAQ, and Schools By Bob Thompson 28 Mechanical Systems Noise in Classrooms By Timothy Foulkes 33 O volatile organic compounds

23、 (VOCs) from out gassing of building components, furniture, cleaning chemicals or pesticides; endotox- ins produced by bacteria; and mycotoxins produced by mold. Respirable airborne particulates, such as fine dust, fungal spores, and potentially infectious droplet nuclei can also be removed from rec

24、irculated air by filtration with effective removal efficiency for particles below 1 O microns in size. Particle dilution effectiveness depends on both the rate of air recirculated and the efficiency of the filters that can be installed. This capability is excellent for constant volume systems equipp

25、ed with medium to high efficiency filters. Room units provide a constant rate of circulation but are normally designed to accommodate only low efficiency filters. Outdoor air is seldom free of contaminants, both gaseous and particulate. The source of outdoor air is often limited. Unit ventilators, f

26、or instance, usually require outdoor air intakes in the perimeter wall of the classroom. Should a loading dock or cafeteria exhaust discharge be near the intake, or if the intake is close to the ground or roof level, the outdoor air may actually introduce pollutants into the classroom. Thermal Load

27、For all-air systems, the supply air rate must be sufficient to offset the design room sensible heat gain or heat loss. Sensible cooling loads for the air-conditioned classroom dictate a supply air rate typically in the range of 0.8 to 1.2 cfm/f+ 4 to 6 L/ (s.m2 for most systems. The room sensible he

28、at factor at design load is usually about 0.75. The grand (machine) sensible heat 12 AS H RAE Journal June 1998 factor varies by climate, but averages about 0.60. These factors usually run some 5% to 10% lower for occupied interior classrooms and perimeter classrooms without solar heat gain. maximum

29、 room relative humidity under any condition of load depends on the average coil surface temperature. The cooling coil and temperature of the cooling medium are selected to deliver supply air at a temperature cold enough to offset the maximum sensible heat gain. Sufficient moisture removal (latent co

30、oling) must also be provided to achieve acceptable humidity within the space. Air supplied to a classroom at 55F (1 3C) is likely to result in 55% to 60% rh under design conditions. Figure 1 illustrates the cooling process under design conditions. constant supply air temperature to zoned reheat cont

31、rolled by room temperature can maintain fairly constant relative humidity during a full range of occupancy. For systems that vary the cooling coil surface temperatures to maintain space tempera- ture (as with a chilled water valve modulating flow to a unit ventilator coil), the relative humidity can

32、 increase to 70% or more at reduced load. Figure 2 diagrams the performance of this type of control with a fully occupied classroom on a rainy day (75F 24T, 90% rh). The relative humidity with a variable air volume, constant supply air temperature system increases about five percentage points as sup

33、ply flow is reduced to the minimum (equal to the minimum outdoor air rate for ventilation). Figure 3 depicts VAV system performance under the same rainy day conditions. Often cooling coils in factory-assembled equipment are designed for high sensible heat factor duty. When applied to low sensible he

34、at factor applications, such as the classroom, a coil selected for the total cooling load may have excess sensible cooling capacity and insufficient latent capacity. This mismatch leads to higher than desirable space relative humidity. On/off control of supply air cooling can result in serious exces

35、sive space humidity and actually add to the space latent load by introducing unconditioned outdoor air and re-evaporating condensed moisture from the cooling coil. Since classrooms do not usually have For any system, the ability to maintain a A constant volume system with a - I - IC -120 4 2 -110 p.

36、 -100 9 - 90 a 5 O 3 - 80 - 70 2 9 - 60 2 O - 50 o z - 40 $ IC U .i lamma IQQA STD. ASHRAE JOURN SUPP I 1 I t I 1 I I I l 1 45 50 55 60 65 70 75 80 85 90 95 DRY BULBTEMPERATURE, “F 1 Figure 1: Classroom ai7, coditionirzg at full cooling load direct control of humidity, the air- conditioning system a

37、nd the provision for room temperature control should be selected to maintain room relative humidity within an acceptable high limit. Designing for a maximum relative humidity of 60% throughout the full range of cooling load conditions, not just during outdoor design conditions, is an important consi

38、deration. In humid climates, provision for humidity control during unoccupied periods may also be necessary to avoid mold growth. Some systems combine a separately conditioned outdoor ventilation air supply with room units, such as fan coil or water source heat pumps, that provide heating and coolin

39、g of the space. This ventilation air supply can be pre-conditioned to a sufficiently low dew point to accomplish most of the room latent cooling. Accept- able room relative humidity is assured as the space temperature control modulates room unit cooling capacity. Auditoriums, Cafeterias, and Gymnasi

40、ums These spaces have high concentrations of students for short periods of time. The short term demand for outdoor air ventilation is high, often in excess of the supply air rate needed to offset the sensible cooling load. The peak room sensible heat factor is quite low, commonly less than 0.7, but

41、the interior latent load is not sustained. Systems distinct from that for the classrooms are generally prescribed. Constant volume, terminal reheat systems are most often dictated by the thermal and ventilation load characteristics. Energy expensive, yes; but demand-controlled ventilation and priori

42、ty control by either space temperature or humidity can substantially cut that burden. If these spaces are heated and ventilated but not mechanically cooled, the classroom system is in many instances capable of providing for them. Food odors in the cafeteria inhibit recirculation of this air through

43、central systems serving other spaces. If there is an adjacent kitchen, cafeteria supply air can contribute to makeup air for kitchen exhaust. Off i ces Offices also have significantly different ASHRAE lournal 13 i JUNE 1778-ENGL 1778 IMi 0757b50 U535b7 bL7 m characteristics than other school spaces-

44、 relatively low ventilation requirement, high sensible heat factor-and are well served by systems suitable for office buildings. Since school offices are in use during the summer, the refrigeration for their cooling should be independent of that serving other spaces not normally occupied during that

45、 season. Commonly, the offices in schools otherwise not air conditioned have unitary air conditioners. System Design Objectives Occupancy characteristics, ventilation, temperature, and humidity control are not the only parameters for selection of school systems. The following other factors are part

46、of the analysis: Indoor Air Quality More than outdoor air ventilation is involved. The total air supplied to a room from a central system dilutes both gaseous and particulate contaminants generated within that room. Conversely, central systems recirculating air can transfer those contaminants, albei

47、t greatly diluted, to other spaces. A few building codes restrict recirculation of air among spaces to prevent this. Mold spores and droplet nuclei containing infectious microbes can be removed from recirculated (and outdoor) air by medium and high efficiency filters. Central air systems can accommo

48、date better filters. Room units, such as unit ventilators and heat pumps, usually cannot. Particulate concentrations in room air are affected by both the degree of filtration and the air circulation rate. Accordingly, constant volume systems are superior to variable air volume or on/off supply air s

49、ystems in this regard. Acoustics The ASHRAE Handbook-Funda- mentah recommends a criterion for classroom sound of NC-30 as an accept- able system noise level for the range of speech communication frequencies. System and equipment selection along with application of sound attenuating techniques are means of limiting HVAC system noise to acceptable levels. Noise from equipment within the classroom, emanating from air outlets or radiating through ceilings, can be disr