ASHRAE AB-10-010-2010 Tight Humidity Control for Flexible Applications.pdf

1、2010 ASHRAE 435ABSTRACTHumidity control of spaces is a traditional HVAC engi-neering process; however we tend to look at these processes in a steady state environment. When dynamics are introduced into the equation the response and performance of a conditioning system become critical. This paper wil

2、l address the condition-ing concepts for a newly designed museum that contains tradi-tional galleries and non traditional spaces all designed to provide different levels of flexibility, yet at the same time provide a system that performs in response to the performance required. The system performanc

3、e described in this paper will address unoccupied building mode as well occupied mode.INTRODUCTIONThe primary purpose of museums Heating Ventilation and Air Conditioning (HVAC) system is to establish and main-tain pre-determined environmental conditions within the building. There are two conditions

4、that govern the interior environment within the building:The first is to ensure that the temperature and humidity conditions maintained in the building are correct for the pres-ervation of the artwork to be exhibited or stored.The second is to create an environment that is satisfactory for the visit

5、ing public.The proper HVAC system for the protection of the exhib-its must address these two key items, minimize the effect that changes in the outside environment will have on the interior of the building and assure that specified interior conditions are maintained at all times.To protect the build

6、ing from being influenced by outside climactic conditions, the building envelope (walls, roof, and windows) must be carefully designed and constructed to mini-mize the effect of changes in weather and climate on the inte-rior of the building, particularly in areas where sensitive works of art are di

7、splayed or stored. This would include thermal performance as well as the porosity or air tightness of the building.Maintenance of the proper interior environment is the function of the HVAC system design. This system is designed to provide a controlled temperature and humidity throughout the year 24

8、 hours each day in the exhibit and storage areas.The building environment is monitored and controlled by a central computerized Building Management System (BMS). The BMS system will monitor and report on all aspects of the operation and automatically create maintenance and trouble shooting documents

9、 to alert the operating staff of actions to be taken to correct an improper environmental condition in the building.The air handling systems will transmit heating and cool-ing from the boiler and refrigeration plant to the various spaces in the building in a manner that will ensure a clean environ-m

10、ent with the temperature and humidity controlled at all times, using air as the transfer medium. For the galleries a variable volume, variable temperature air supply system together with a radiant floor for heating and cooling will be utilized. The air handling system will be sepa-rate from the non

11、critical areas of the building. It will therefore be possible to operate and occupy administrative, storage, restoration and other support areas separate from exhibit areas utilizing variable air volume systems for energy efficiency.Simmonds (1994) reported on using radiant floors for both heating a

12、nd cooling to condition museum spaces. Akron Art Museum and the Water and Life Museum in Hemet, Cali-fornia have been successfully conditioned in the same manner. Tight Humidity Control for Flexible ApplicationsPeter Simmonds, PhD Patrick WilkinsonFellow ASHRAE John Gautrey Jacques de PastreAssociat

13、e Member ASHRAEPeter Simmonds is a senior associate and Patrick Wilkinson is an engineer in the Advanced Technology Group, and John Gautrey is a part-ner at IBE Consulting Engineers in Sherman Oaks, CA. Jacques de Pastre is a partner at IBE France Consulting Engineers in Paris, France.AB-10-0102010,

14、 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs

15、 prior written permission.436 ASHRAE TransactionsThe same principles have been used in these designs with the exception of the perimeter air supply.With the advances in simulation programs which permit detailed analysis of the indoor environment, the individual elements necessary for the creation of

16、 a comfortable indoor climate can be analyzed and optimized. Using the predicted mean vote as determined by Fanger (1972), radiant heat exchange can be studied. Since each individual surface temperature and its relationship (i.e. position to the other surfaces) can be determined, a solution to the c

17、omfort balance equation can easily be found.When incorporating a radiant system and a variable volume ventilating system, the ventilation system may only be dimen-sioned to supply of outdoor air for each person and to remove the latent as well as the material heat load if a radiant system is selecte

18、d to remove the remaining cooling loads. Simmonds (1993,1994,2003) has reported on these designs and their effec-tiveness in providing optimal climate and comfort.Borressen (1994) and Simmonds, Gaw, Holst and Reuss (2000) have shown that radiant cooled floors are capable of removing up to 85 w/m2 (3

19、0 BTUH/sf) of energy from a space by the combination of 35m/w2 (12 BTU/sf) by convection and 50 w/m2 (17 BTUH/sf) by solar absorption. Many papers have been written on the performance of radiant floor for heating Maccluer, Athienitis, Simmonds, Olesen, Meirhans have reported on the performance of ac

20、tive concrete systems.USAGE PROFILESThe following table shows the assumed daily profiles (see table 1) for space equipment loads, and lighting for the room:Internal Heat GainsLighting.Occupants. The metabolism of occupants would produce 70 W/person (250 BTU) sensible and 70 W/person (250BTU) of late

21、nt heat. The occupants will have a clothing value of 1.0, and an activity level of 1 met. Internal GainsComfort ConditionsTypical design comfort conditions for the internal areas of the building are as follows:Ventilation RequirementsEach occupant is provided with 30m3/h (8 l/s/person) (20 CFM) of o

22、utside air. The total air supplied will meet the maxi-mum ventilation demand. The occupancy is based on the indi-vidual occupant room total.The ventilation rate of outside air is controlled by moni-toring the CO2 levels in the spaces.FiltrationAir filtration is provided in each system to ensure inte

23、rnal air quality. Non-Museum spaces are provided with 30% pre-filters and 85% final filters, rated per ASHRAE 52-76 standard test method. Due to the high concentration of air borne partic-ulate matter in the outside air a separate dusting filter is provided on the outside air intake.Gallery, and art

24、 storage spaces are provided with a combi-nation of carbon bed, activated carbon and potassium perman-ganate filters to control gaseous concentration levels. Time of Day Usage Level00.00 - 08.00 0%08.00 - 18.00 100%18.00 - 24.00 0%SpaceLighting loads (max)% Gain to Return / Exhaust AirGalleries50 W/

25、sq m (5W/sf)50Individual Enclosed Offices12 W/sq m (1.2 W/sf)50Lobbies, Foyers, Corridors8 W/sq m (0.8W/sf)0Forum50 W/sq m (5W/sf)0Space Occupants/AreaHeat Gain Sensible / LatentGalleries 5/2.5/1 sq m/person (50,25 and 10 sf pp)70 W/70 W (250 BTU/ 250 BTU)Space Misc.% Gain to Return / Exhaust AirGal

26、leries20 W/sq m (2W/sf)100Space FunctionWinter Temp (C)Summer Temp (C)Noise Level (NR)Fresh Air RatesHumidity (%)Galleries221 (C) (72F+/- 2F)PMV 0.5241 (C) (74F +/- 2F)PMV 0.525-3030m3/h or 8 l/s. person20 CFM pp50% +/- 2% RH2010, American Society of Heating, Refrigerating and Air-Conditioning Engin

27、eers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.2010 ASHRAE 437The following criterion serve

28、s as a base line concentration levels for selection of filter media:Sulfur Dioxide 0.38ppbNitrogen Oxides 2.5ppbOzone 12ppbHydrochloric acid, acetic acid and formaldehyde are also controlled. To this end the building is to be flushed with 100% outside air with new filters in the units for a period t

29、o be deter-mined prior to the installation of artwork to remove VOCs from the construction materials.AIR DISTRIBUTIONMultiple air handling units are provided to distribute conditioned air to various spaces within the building. The units are variable volume for the galleries, lobby and forum. Each un

30、it includes filters (high efficiency and medium efficiency particulate, carbon and chemical as appropriate), pre-heat coils, chilled water coils, heating coils, humidification section, supply fan, return fan economizer and controls. Air handling unit controls are arranged to conserve energy by provi

31、ding for an “occupied“ and “unoccupied“ mode of operation. The occupied mode provides full system operation. The unoccupied cycle reduces the supply air quan-tities to the minimum level required to maintain the environ-ment required for the exhibits and also shuts down the ventilation systems and li

32、ghting systems. In addition Carbon dioxide concentrations are monitored to reduce the levels of outside air when limits are being met. Each economizer is provided with dual outside air dampers and outside air flow stations to facilitate better control of outside air quantities and building pressuriz

33、ation.Air outlets are provided for supply and return of condi-tioned air to the space at low velocity. The air supply slots for this design were somewhat different than previously used. Horizontal supply slots have been successfully used at Akron Art Museum and the Water and Life Museum in Hemet, Ca

34、lifornia.The challenge for this particular design was to ensure the ventilation air was sufficient for the occupants and at the same time provide an even distribution of humidity and temperature throughout the space for the variations in loads and occupancies.The perimeter slot would be 5cm (2 inche

35、s) wide (see figure 1) and would encompass the perimeter with the excep-tion of the two doors in the gallery. The air will be dispersed upwards through a 70% perforated plate to ensure an even distribution along the slots. From similar designs we know the air would ventilate the perimeter areas, but

36、 what about the middle of the space and how would the temperature and humidity levels be distributed throughout the space. The first step was to analyze the space conditions and mean radiant temperatures in the space. The mean radiant temperatures were important as the major conditioning system in t

37、he space would be the radiant floor for both heating and cooling. The second step is use analyze the space conditions using Compu-tational Fluid Dynamics. The results would hopefully show how the air distribution was functioning and the distribution of temperature and humidity levels. Gallery Condit

38、ioningEach Gallery will be supplied with sufficient air to main-tain a space temperature of +/- 22C(+/-72F) by supplying air at 17C (63F) from low level. The maximum volume of supply air has been calculated to maintain the required space Table 1. Monthly Variation in the Hourly Total Visitor Occupan

39、cyHour 10 11 12 13 14 15 16 17 18 19 20 21Jan. 100 300 380 550 740 740 740 740 740 570 200 0Feb. 95 284 359 520 700 700 700 700 700 539 189 0March 121 363 459 665 894 894 894 894 894 689 189 0April 116 347 440 637 857 857 857 857 857 660 232 0May 122 367 465 674 906 906 906 906 906 698 245 0June 386

40、 489 707 951 951 951 951 951 951 733 257 0July 120 359 455 659 887 887 887 887 887 683 240 0Aug. 109 326 414 599 805 805 805 805 805 620 218 0Sept. 127 382 484 700 942 942 942 942 942 725 255 0Oct. 131 392 496 719 967 967 967 967 967 745 261 0Nov. 113 339 429 621 836 836 836 836 836 644 226 0Dec. 11

41、1 333 422 610 821 821 821 821 821 633 222 02010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print

42、or digital form is not permitted without ASHRAEs prior written permission.438 ASHRAE Transactionstemperature with a maximum 50W/m2 (5W/sf) of lighting and the following occupancies:1 person per 5m2 (50 sf)1 person per 2.5m2 (25 sf)1 person per 1 m2 (10 sf)Each space will have a temperature sensor in

43、stalled in the Gallery space. Space setpoint temperatures of 21-23C (71-73F) are maintained by varying the supply temperature and volume as well as the output from the radiant floor (see figure 2).Humidity control in the Galleries is a little more compli-cated. The humidity level in each space is mo

44、nitored by space humidistats, typically four in each gallery. The humidity level in each Gallery is relayed to a central control unit. Based upon either the lowest or highest humidity level, the moisture control of the supply is either increased or decreased accord-ingly. The humidity level of the s

45、upply air is increased by introducing steam heated by electricity into the supply air stream. To decrease the moisture level of the supply air, the supply air is cooled to a temperature below the supply temper-ature but to moisture content in gr/kg. The supply air is then heated to the supply temper

46、ature required to maintain space temperature within the required set points of 21-23C (71-73F).The humidity levels in the galleries will only vary depend-ing upon the latent heat produced by the occupants (figure 3). None of the galleries has external openings and therefore any infiltration of possi

47、bly humid outside air is eliminated. The heat given off by the maximum number of space occupants is calcu-lated and the level of moisture in grains per pound is plotted on Figure 1 This shows the details of the supply slot. The velocity of air through the slot will vary between 0.39 m/s (70 fpm) to

48、4.46 m/s (802 fpm).Figure 2 The internal dry bulb temperatures for a gallery having different occupancies. The combination of radiant floor and supply are able to maintain the required temperature throughout the occupied period.2010, American Society of Heating, Refrigerating and Air-Conditioning En

49、gineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.2010 ASHRAE 439a psychometric chart. The supply air condition is then calcu-lated at a conditioned in gr/kg, that when increased by the maxi-mum moisture production of the occupants does not exceed the maximum allowable space humidity levels.PERMANENT GALLERYThe permanent Gallery will have radiant floor for heating and