Climatic applicability of downdraught evaporative cooling in the United States of America
Introduction
The building sector accounts for a significant part of the global energy consumption. For decades, space heating and cooling (space conditioning) accounted for more than half of all the residential energy consumption [1]. In recent years, further progress has been made in the identification and implementation of energy demand reduction strategies in buildings. This trend was created by an increased adoption of more efficient equipment, better insulation, more efficient windows, and population shifts to warmer climates [2]. This shift in how energy is consumed in homes has seen that even if per-household energy consumption has steadily declined, more homes are using air-conditioning than in the past.
According to the U.S. Energy Information Administration (EIA), the Residential Energy Consumption Survey [3], nearly 9 out of 10 U.S. homes are air conditioned by central units, individual units, or both. On the other hand, other solutions, including use of fans, dehumidifiers, and pool pumps, also increase summer electricity use in homes. In the U.S., the monthly electricity consumption peaks are in July and August when temperatures and cooling demand are the highest. The EIA estimates that 18% of annual household electricity use are for air conditioning. Three-quarters of all air-conditioned homes use central equipment, but individual air-conditioning units are more common in the cold to very cold climate regions in the northern United States and the marine climate region along the West Coast. In Fig. 1 the use of this systems is shown by climatic regions.
Various techniques have been implemented to improve the building energy efficiency. Traditional air-conditioning methods, such as heat pumps and boilers, are mostly active strategies. However, air conditioning is recognized as a significant factor in global warming and climate change [5]. On the other hand, there is a growing interest in utilizing passive and low-energy systems for cooling buildings, both residential and commercial. Moreover, according to the U.S. Energy Information Administration (EIA), the Commercial Buildings Energy Consumption Survey [6], the country has 5557 thousand of Commercial buildings. Divided in four census regions, where all the building use heating energy sources, and a high percentage of buildings with cooling energy sources (Fig. 2).
HVAC are conventional means of creating thermal comfort, however, they are energy intensive and less ecological. Passive cooling can be adopted as a viable alternative, because these technics can remove heat sensibly if the air is cooler or by evaporating water if it is dry [7]. In the search for alternatives, passive downdraught evaporative cooling (PDEC) is proving to be both technically and economically viable in different parts of the world [5]. Following the theoretical and experimental work by Baruch Givoni in Israel, and by Cunningham and Thompson in Arizona, a number of pioneering buildings adopting this innovative technique have emerged around the world [8]. In the last years, the Passive and Hybrid Downdraught Evaporative Cooling (DEC) is a viable alternative to conventional mechanical cooling in buildings. These first-generation buildings demonstrate the technical applicability of Passive and Hybrid DEC as part of a climatically responsive approach to design and to the provision of comfort [8]. Different simplified simulation models of a PDEC have been developed and compared. The results could help designers in choosing amid different calculation models [9].
The downdraught cooling solutions are classified into three types:
- (1)
The Passive Downdraught Evaporative Cooling (PDEC): when downdraught is achieved through the evaporation of water within an air stream. The passive cooling refers to the exploitation of an ambient heat sink to achieve cooling. The idea is based on the fact that the latent heat of water evaporation is absorbed from the passing hot-dry air stream. The process is an adiabatic humidification process in which part of the sensible heat of the air stream is transferred to latent heat. Therefore the sensible heat of the air stream decreases and its DBT decreases, while on the contrary, its latent heat increases, and as a result, the air supplied is not only cooler, but is also more humid. Due to this, it is used as a passive cooling system or part of a complex cooling system. This system works as a complete passive cooling, because in general, no active parts are added (such as pumps or fans). However, when there is no wind and the downdraught airflow relies solely on buoyancy forces, this solution is not feasible, and in this case needs to use fans to enhance the air distribution.
- (2)
The active downdraught cooling (ADC): when the cooling is achieved by using chilled water cooling coils or panels, driving air over evaporative cooling pads directly into the building, which means the strategy relies on mechanical cooling. This technique is an alternative to conventional air conditioning that can contribute to reduce the energy consumption because only the mechanical system needed for the air-cooling is responsible of this energy consumption.
- (3)
Hybrid downdraught cooling (HDC): when it combines both ‘passive’ and ‘active’ downdraught cooling techniques. This technique is an alternative to conventional air conditioning that can contribute to reduce the energy consumption because only needs alternatively, the mechanical system needed for the air cooling, or the fans required for the air circulation and distribution.
These techniques have a good potential to provide an alternative to conventional air conditioning systems offering comparable comfort levels with reduced energy consumption and therefore reduced greenhouse gas emissions. Evaporative cooling techniques have been proved feasible both from economic and technical stand points through numerous studies, nevertheless their efficiency can dramatically be reduced in the case of hot humid climates [10]. The systems use evaporative cooling in hot and dry conditions and chilled water cooling coils in warm and humid conditions [11].
In the case of the U.S., it is possible to derive in which parts of the country these techniques can be applied, and the potential of the application, taking into account the climatic data of the meteorological databases known in this country. The high potential for application of these techniques in buildings could reduce their energy impact substantially.
In this article the applicability of the above-mentioned innovative solutions is going to be studied within the United States of America.
Section snippets
General climate classification in U.S.
The United States is the world's fourth largest nation by total area, with its large size and geographic variety, it includes most climate types. The specific climatology of each county is shown in Fig. 3, according to the Köppen climate classification, Table 1, [12].
Approximately, to the east of the 100th meridian, the climate ranges from humid continental in the north to humid subtropical in the south. The Great Plains west of the 100th meridian is semi-arid. Much of the Western mountains
Map of downdraught cooling
The following applicability maps are conceived to give architects and engineers an overview of the appropriate downdraught cooling strategies during the initial conceptual stage of the design.
The methodology followed has been described previously in chapter 6 of a manual on downdraught cooling [11]. Following that publication [11], more detailed applicability studies were developed for Europe and China, but never for the U.S. Other authors purpose to assess the applicability of an indirect
Map of intervention categories
The applicability in terms of priority of intervention in the case of the U.S. can be defined by comparing the maps in Fig. 5 and Fig. 6. The comparative analysis of these maps is shown in Table 2. The potential for cooling varies among different regions and over time at a specific location. These variations must be assessed in order to decide upon the feasibility of applying evaporative cooling in a proposed building projects. For example, a location in the zone 1 in terms of climatic
Map of cooling degree days and its relation to downdraught cooling design strategies
Cooling degree days represent the number of degrees and days where the outside temperature is higher than the base temperature. Cooling degree days can be used to help assess or compare different potential sites for development of cooling strategies. They can also be used as a way of normalising weather between different sites, allowing a comparison of the performance of different buildings. The use of degree days should be treated with caution as part of a broader process of analysis,
Applicability analysis in real buildings
In order to validate the mapping approach and verify the applicability predictions, a more detailed analysis of the climatic applicability of downdraught cooling in relation to the performance of buildings that have implemented this type of system in different climatic conditions was undertaken. Four pairs of buildings and counties were selected: Sonoma (building 1) and Stanford (building 2) in the state of California, Washington (building 3) in Utah and Maricopa (building 4) in Arizona. The
Conclusion
New applicability maps and a climate classification of the potential for downdraught cooling in U.S. have been presented in this paper. The developed maps and classification have been based on (DBT–WBT), cooling degree hours and (26ºC-WBT) indexes.
Using a bioclimatic approach, the potential use of downdraught cooling was analyzed in four counties and the results showed that the map of intervention categories developed concurred with the symmetric analysis of Givoni for evaporative cooling,
References (36)
- et al.
Passive alternatives to mechanical air conditioning of building: Areview
Build. Environ.
(2013) - et al.
Direct evaporative passive cooling of building. A comparison amid simplified simulation models based on experimental data
Build. Environ.
(2015) - et al.
Climatic cooling potential and building cooling demand savings: high resolution spatiotemporal analysis of direct ventilation and evaporative cooling for the Iberian Peninsula
Renew. Energy
(2016) Options and applications of passive cooling
Energy Build.
(1984)- et al.
Evaluating the potential of an indirect evaporative passive cooling system for Brazilian dwellings
Build. Environ.
(2015) - et al.
A bioclimatic approach to develop spatial zoning maps for comfort, passive heating and cooling strategies within a composite zone of India
Build. Environ.
(2018) - et al.
Summer discomfort reduction by direct evaporative cooling in southern mediterranean areas
Energy Procedia.
(2017) - et al.
Derivation of the adaptive equations for thermal comfort in free-running buildings in European standard EN15251
Build. Environ.
(2010) - et al.
Post-occupancy evaluation: state-of-the-art analysis and state-of-the-practice review
Build. Environ.
(2018) - et al.
Using the Köppen classification to quantify climate variation and change: an example for 1901-2010
Environ. Dev.
(2013)
Comfort, climate analysis and building design guidelines
Energy Build.
Annual Energy Outlook 2017
Quadrennial Technology Review: an Assessment of Energy Technologies and Research Opportunities
Residential Energy Consumption Survey (RECS); Using the 2009 Microdata File to Compute Estimates and Standard Errors (RSEs)
Passive downdraught evaporative cooling: principles and practice
ARQ Archit. Res. Q.
Commercial Buildings Energy Consumption Survey ( CBECS ) User's Guide to the 2012 CBECS Public Use Microdata File
Post-occupancy evaluation of non-domestic buildings using passive downdraught evaporative cooling in south-west USA
Architect. Sci. Rev.
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Technological adaptation zone of passive evaporative cooling of China, based on a clustering analysis
2021, Sustainable Cities and SocietyCitation Excerpt :Other scholars also use relative humidity to evaluate the Pablo A of evaporative cooling equipment. According to the dry ball temperature and the wet bulb temperature, the feasibility of evaporative cooling technology in the United States was determined (Aparicio-Ruiz, Schiano-Phan, & Salmerón-Lissén, 2018). The potential for the use of direct evaporation cooling in the Mediterranean region has been analyzed, and results show that the temperature difference between wet and dry balls is better than that of wet balls as an evaluation index, in terms of the degree of the impact of technology used (Chiesa, Huberman, & Pearlmutter, 2019).
Using the sky as heat sink: Climatic applicability of night-sky based natural cooling techniques in Europe
2020, Energy Conversion and ManagementCitation Excerpt :Finally, they assessed the potential savings by running EnergyPlus simulations of an office building selected as a representative building. Aparicio-Ruiz et al. [27] analysed the potential applicability of downdraught cooling in the USA. Their approach was based on a set of maps derived from two related climatic indexes: dry bulb temperature to wet bulb temperature depression (DBT − WBT), representing the climatic opportunity; and 26 degreesC minus wet bulb temperature (26 degreesC − WBT), representing the climatic opportunity against the theoretical cooling requirement for each location.
Contrasting climate-based approaches and building simulations for the investigation of Earth-to-air heat exchanger (EAHE) cooling sensitivity to building dimensions and future climate scenarios in North America
2020, Energy and BuildingsCitation Excerpt :This approach allows to calculate the reduction in cooling degree hours (CDH) due to evaporative cooling systems and the reduction in number of discomfort hours in respect to local weather data. Similarly, Salmeron et al. [26] and Ford et al. [27] defined a climate potential approach that was applied to Europe [26], China [28] and recently to U.S. [29]. These examples highlight the utility, and motivation for further development, of climate based pre-design approaches for determining the potential for climate dependent passive cooling approaches.
Thermal performance prediction of office buildings using direct evaporative cooling systems in the composite climate of India
2019, Building and EnvironmentCitation Excerpt :The potential for application of direct evaporative cooling depends on climatic characteristics particularly the wet bulb depression [43,56]. Following the classification proposed for assessing the applicability of direct evaporative cooling from ‘very low’ to ‘very high’ based on ambient wet bulb depression [79], authors have graphically presented the applicability categories for Jaipur climate in Fig. 14. Peak summer months of April, May, and June, more than 70% of the time thermal discomfort prevails in the outdoor environment.
Geo-climatic potential of direct evaporative cooling in the Mediterranean Region: A comparison of key performance indicators
2019, Building and EnvironmentCitation Excerpt :In contrast, methods that are based on an hourly calculation can provide a more detailed definition of the local geo-climatic applicability of DEC solutions. Two such approaches are introduced here (termed “Method B” and “Method C”, respectively), and are compared with Method A (the seasonal method [57]) as well as with results from dynamic simulations using EnergyPlus (US Department of Energy and the National Renewable Energy Laboratory) to model a sample office room. This comparison focusses on the Mediterranean region, within which climate variability is known to create a situation in which many locales are sufficiently warm and dry for DEC to be effective over much of the year.