1、2009 ASHRAE 573ABSTRACTThis paper shows the feasibility of harvesting condensate from large dedicated outdoor air handling units and applying the condensate to effectively reduce the annual projected pota-ble water consumption for a case study building. Condensate production potentials are calculate
2、d for three areas in Texas; San Antonio, Houston, and Dallas / Fort Worth. A case study building is presented, for which the production potential is applied. The case study building annual condensate produc-tion as well as the annual potable water consumption for the water closets and urinals and co
3、oling tower makeup water is calculated and presented to compare condensate supply and potable water demand. The case study building, which is a medical research laboratory located in San Antonio, TX, was determined to have an annual condensate production of 1,887,031 gallons (7.15 x 106L), which wou
4、ld normally be sent to the sanitary sewer system. The analysis indicates that the condensate production from the case study buildings large dedicated outdoor air handling units can completely supple-ment the annual water closet and urinal water demand with 1,614,031 gallons (6.12 x 106L) of excess,
5、which could be used to supplement landscape irrigation system or the entire condensate production could be applied to reduce the cooling tower makeup potable water demand by an estimated 16%. INTRODUCTIONWith the adoption of building service systems requiring designs to minimize their environmental
6、impact, innovative as well as obvious natural resource conservation measures are being explored. One element of conservation considered in design is to minimize water usage in buildings. Modern designs often use green design practices suggested by organizations like the US Green Building Council and
7、 their LEED new construction guidance, where points toward receiving an overall rating are assigned to reducing annual water consumption by 20% and 30% from a baseline fixture flow rates determined by the Energy Policy Act of 1992 (USGBC, 2007). Hydronic systems makeup for equipment such as cooling
8、towers is not generally included in building baseline water consumption rates for LEED, however should be considered in whole build-ing water consumption estimates. Typical water conservation measures are utilizing low and zero flow fixtures, utilizing grey water for non-potable uses, and minimizing
9、 high water demand landscaping. Other, less common, water conservation measures utilizes the harvesting of water producing sources to offset the annual water consumption to achieve a net annual water reduction. These water producing sources include storm water recovery and air conditioning condensat
10、e harvesting.Condensate from air conditioners, dehumidifiers, and refrigeration units can provide facilities with a steady supply of relatively pure water for many processes. Laboratories are excellent sites for this technology because they typically require dehumidification of large amounts of 100%
11、 outside air (DOE, 2005).Another element considered in building design is indoor air quality and building envelope pressurization. Ventilation for Acceptable Indoor Air Quality, ASHRAE Standard 62.1-2004 recommends appropriate ventilation levels for various building and occupancy types. If buildings
12、 have excessive exhaust requirements due to fume hoods, user required air change rates, or other process exhaust, the Condensate Harvesting from Large Dedicated Outside Air-Handling Units with Heat RecoveryFrank L. Painter, PEAssociate Member ASHRAEFrank L. Painter is a mechanical engineer with the
13、U.S. Army Corps of Engineers, Fort Worth District, San Antonio Construction Management Office, San Antonio, TX.LO-09-054 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use o
14、nly. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.574 ASHRAE Transactionsminimum ventilation air requirements are potentially higher. Outdoor ventilation air commonly contains a higher moisture concen
15、tration and temperature than what is desired in the space. Conditioning this air by both reducing the temperature as well as reducing the moisture content is required. Because some designs require increased levels of outside ventilation air for a variety of reasons, the potential to recover the ener
16、gy being expelled by the exhaust system and transfer to the incoming ventilation air is high. Due to this potential, ASHRAE has incorporated policy regarding energy recovery, outlined in the Energy Standard for Buildings except Low-Rise Residential Buildings, ASHRAE Standard 90.1. To satisfy ASHRAE
17、90.1, fan systems that have a design air flow rate of 5000 cfm (2358 L / sec) or greater and have a minimum outside ventilation air flow that is equal to 70% or more of the supply air shall have an energy recovery system with at least 50% recovery effectiveness (ASHRAE, 2004). There are exceptions t
18、o this requirement, however for the purpose of this paper, no exceptions are taken.To centralize the process of pre-conditioning ventilation air and the recovery of exhaust air energy, large energy recov-ery units or DOAHUs with energy recovery means are commonly used. These units are designed to pr
19、ovide pre-conditioned ventilation air either directly to the occupied space or ducted to an additional AHU. All building exhaust is also ducted to these units, which exchanges sensible and latent energy with the incoming ventilation air. There are several types and configurations of DOAHU available
20、for use. They have heat recovery means, either by an enthalpy wheel, glycol run around loop, air-to-air heat exchanger, or others. In addition, they often have cooling and heating coils, as well as humidifiers depending on the appli-cation. The type of DOAHU studied in this paper is one with an ener
21、gy recovery device, pre-heat and cooling coil down-stream of the recovery device, and a heating coil in the reheat position, shown in Figure 1.These units pre-condition large quantities of moisture laden air down to a more moisture neutral state, where the humidity ratio1is close to the delivered su
22、pply air humidity ratio. This process produces large quantities of condensate, which is commonly discharged to the sanitary sewer systems. Some water treatment facilities operate at near capacity and do not allow or discourage condensate disposal into the sanitary sewer system (ICC, 2006).The focus
23、of this paper is to determine the feasibility of coupling both the water conservation and indoor air quality and building envelope pressurization elements of design by harvesting air conditioning condensate for non-potable water supplementation in large commercial, institutional, and medi-cal buildi
24、ngs, where large volumes of outside air are required. METHODOLOGYThe first step in the analysis was to gather temperature and humidity data for several geographical regions in Texas. The areas chosen for study were north Texas represented by Dallas, central / south Texas represented by San Antonio,
25、and east Texas represented by Houston. The data used was annual daily average dry bulb temperature and relative humidity data obtained using an online weather archiving site. Since conden-sation production is the focus of this paper, outside air temper-atures of 65oF (18.3oC) or below are excluded i
26、n the analysis. In highly humid climactic zones where deep de-humidifica-tion is used to prevent mold and mildew, additional water production may be realized at temperatures as low as 55 oF. All remaining data was used to calculate the average humidity ratio for each day using the following equation
27、s.Eq. 1 determines the saturation pressure of the water vapor in the air as a function of the dry bulb temperature in the absolute scale of either Rankine or Kelvin. (1)where = dry bulb temperature, R (K)= saturation pressure of water vapor, psia (Pa)The saturation pressure is used to calculate humi
28、dity ratio using Eq. 2. (2)where= humidity ratio, lbv/lba(gv/kga)= atmospheric pressure, psia (kPa)= relative humidity, %Once the humidity ratios based on the daily average dry-bulb temperature and relative humidity level are calculated, the annual performance of the AHU is evaluated. The first calc
29、ulation performed was to determine the leaving enthalpy wheel air conditions using Eq. 3 and Eq. 4. The recovery effec-tiveness was initially modeled at the ASHRAE 90.1 minimum effectiveness of 50%; however total enthalpy wheels can have a sensible and latent effectiveness as high as 75% (VanGeet an
30、d Reilly, 2006). The higher the latent recovery effectiveness is, the lower the moisture content in the air entering the cooling coil is, which ultimately reduces the amount of condensate produced. The return air temperature is assumed during cool-ing days to be 75oF (23.4oC) at 55% RH, since this o
31、perating point is very common for Texas and falls within the acceptable 1.Humidity ratio is defined as for given moisture sample it is the ratio of the mass of water vapor to the mass of dry air in the sample (ASHRAE, 1993).Ln pws()C1Tdb- C2C3+ TdbC4+ Tdb2C5Tdb3C6Ln Tdb()+=Tdbpws 0.62198pwspatmpws-1
32、00-=patmASHRAE Transactions 575range of operating temperature and humidity level defined in ASHRAE 55-2004. The assumed return air condition does not account for any sensible gain during transport back to the DOAHU.(3)(4)where= temperature leaving enthalpy wheel, entering cooling coil, F (C)= humidi
33、ty ratio leaving enthalpy wheel, entering cooling coil, lbv/lba(gv/kga)= enthalpy wheel sensible recovery effectiveness= enthalpy wheel latent recovery effectiveness= return air temperature from building, F (C)= return air humidity ratio, lbv/lba(gv/kga)= outdoor air temperature, F (C)= outdoor air
34、humidity ratio, lbv/lba(gv/kga)The next step is to determine the humidity ratio for the cooling coil leaving dry bulb temperature and relative humid-ity. It is assumed that the cooling coil leaving conditions is a 55oF (12.8oC) dry bulb temperature with a 90% relative humidity. This assumption is ma
35、de since a cooling coil leave temperature of 55oF (12.8oC) and essentially saturated at 90% RH would provide adequate dehumidification and supply dry enough air to account for any latent gain encountered in the space. This assumption also implies that the entering air humidity ratio is not less than
36、 the assumed cooling coil leaving air humidity ratio, resulting in a dry-coil. The final step is to calculate the condensate production potential from the dehumidification process. Condensate production potential represents the potential for condensate production per cubic feet of treated air flow.
37、Condensate production potential is calculated using Eqs.6 and 7 to be applied to any dedicated outdoor air handling unit with similar configuration and performance characteristics. To determine the condensate production rate for a specific air flow quantity, simply multiply the air flow rate by the
38、condensate production density using like units.(5)Table 1. Saturation Pressure Constants forI-P and SI UnitsConstants I-P Units SI UnitsC11.044 1045.800 103C21.130 1015.516 100C32.702 1024.864 10-2C41.289 1054.176 105C52.478 1091.445 108C66.546 6.546Figure 1 Diagram of dedicated outdoor air-handling
39、 unit with enthalpy-wheel-type heat recovery.TECCsTRATOA1 s()+=ECCLRAOA1 L()+=TECCECCsLTRARATOAOAccECCLCC=576 ASHRAE Transactions(I-P) (6)(SI) (7)where= change in humidity ratio across the cooling coil, lbv/lba(gv/kga)= cooling coil leaving air humidity ratio, lbv/lba(gv/kga)= density of dry air, lb
40、a/ft3(kg/m3)= condensate production potential, gal/ft3a(Lv/La)Figures 2 and 3 show the condensate production poten-tials for San Antonio, TX, Houston, TX, and Dallas / Fort Worth, TX in 2007. Figure 2 shows the average daily potential for each location in 2007. Figure 3 show monthly averages for 200
41、7, which produces a more easily interpreted plot. In Hous-ton and San Antonio, TX the maximum average monthly condensate production potentials were approximately 6.0 x 10-5gal / ft3a(8.0 x 10-6Lv/ La) and 5.6 x 10-5 gal / ft3a(7.5 x 10-6Lv/ La) respectively, occurring in mid August, 2007. The averag
42、e condensate production potential for Dallas / Fort Worth was 5.0 x 10-5gal / ft3a(6.7 x 10-6Lv/ La) occurring in early to mid August, 2007.CASE STUDYBuilding DescriptionThe case study building was a large medical research laboratory located in San Antonio, TX. Building parameters were obtained usin
43、g the contract documents. The cooling is provided using a 1400 ton capacity chilled water system and the heating is provided using a combination of low pressure steam and hot water. The hot water is produced using a steam to water heat exchanger. Both hydronic systems employ the use of variable freq
44、uency drives on all distribution pumps. The air delivery is provided using six energy recovery units (ERU) and two traditional variable volume air handling units, located in the building penthouse on the fifth floor. The two variable volume air handling units are ignored in this paper since they are
45、 not dedicated outdoor air handling units; however the harvesting of condensate from these types of units is a poten-tial future paper topic. Three of the six ERUs are enthalpy wheel types and three are glycol run around loop style heat recovery. One of each type of ERU is a stand-by unit. For the s
46、implicity of this paper, the ERUs are modeled as one unit, all with the same recovery effectiveness. The maximum total outside air processed through the ERUs is 110,000 cfm (51700 L / sec). The total recovery effectiveness was modeled at 59%, with a sensible and latent effectiveness on 73% and 33% r
47、espectively calculated using procedures defined in ARI Stan-dard 1060-2005. Based on these system characteristics and using the San Antonio, TX condensate production density, adjusted for the new sensible and latent effectiveness, the monthly condensate productions are shown in Figure 4, with a tota
48、l annual estimated production of 1,887,031 gallons (7.15 x 106L).What to Do with the Condensation Collected?Two possible uses for the condensate water collected are explored. The first is water closet and urinal supplementation and the second is cooling tower makeup water usage. Water Closet and Uri
49、nal Usage. The case study building has a designed full time occupancy level of 250 people. Based on the occupancy level, the annual domestic water consump-tion for the water closets and urinals was calculated and was compared to the estimated annual condensate production quantity. It was assumed that 50% are male and 50% are female. To determine the estimated daily water consumed by water closets and urinals, Eq. 8 was used:(8)= daily water consumption, gal (L)= male occup
