Energy saving potential of an air treatment system for improved building indoor air quality in Singapore

Energy saving potential of an air treatment system for improved building indoor air quality in Singapore

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Energy (2017) 000–000 283–288 EnergyProcedia Procedia143 00 (2017) www.elsevier.com/locate/procedia

World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference, WES-CUE 2017, 19–21 July 2017, Singapore

Energy saving an air treatment system improved The 15thpotential InternationalofSymposium on District Heating andfor Cooling building indoor air quality in Singapore Assessing the feasibility of using the heat demand-outdoor a a X. Cuifunction , B. Mohanfor , M.R. Islama,b, S.K.district Choua and K.J.demand Chuaa,b* forecast temperature a long-term heat Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore a,b,c a a b c c b Engineering Science Programme, National University of Singapore, 9 Engineering Drive 1,Singapore 117575, Singapore

a

I. Andrić

*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre

a

IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract

The design of air conditioning mechanical ventilation (ACMV) system affects the building energy performance and the indoor pollutant removal process. The present study aims to reduce energy consumption on ACMV systems by employing a renewable Abstract air treatment system (ATS). The ATS is able to purify the recirculated air through the ozone-based oxidation process and air scrubbing devices. The air purification performance of primary equipment in the ATS has been studied in order to demonstrate District heating networks are air commonly addressed in air thepurification literature asprocess, one of the theATS mostallows effective solutions for of decreasing the the capability to remove indoor pollutants. Due to the a reduced supply outdoor-air greenhousetogas emissions fromload. the building sector.theThese systems require high investments which are returned through the heat translating a lower cooling In addition, reduced outdoor-air fraction results in an improved chiller efficiency. sales. DuethetoATS the is changed conditions and building renovation heat demand in the could decrease, Therefore, capableclimate of achieving marked energy savings because policies, of the reduced cooling load for future conditioning outdoor prolonging the investment return period. airflow. The proposed ATS is particular adept during a period when Singapore faces periodic bad haze situations. Activating the The while main scope of thisthe paper is to assess the feasibility using the solution. heat demand – outdoor temperature function for heat demand ATS decreasing outdoor-air fraction can be anofattractive Based on Singapore climatic condition, an energy forecast. Theanalysis districthas of been Alvalade, in Lisbonthe(Portugal), was potential used as of a case study. The district is consisted of 665 consumption carriedlocated out to estimate energy saving the proposed ATS with varying outdoor-air buildings vary in both construction typology. (low, medium, and three district intake. Thethat “plug-and-play” ATS can beperiod easily and integrated intoThree any weather new or scenarios existing ACMV systems high) to realize immediate renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were improvement in indoor air quality and building energy efficiency. compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications error annual Published demand was lower than ©(the 2017 TheinAuthors. by Elsevier Ltd.20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenariosEnergy combination considered). Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Symposium & The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Forum: Low Carbon Cities & Urban Energy Joint Conference. decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function increased 7.8-12.7% per decade (depending on the Keywords: Air-conditioning; Building energy consumption; Cooling load;intercept Ventilation; Indoor airfor quality. coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: + 65 6516 2558; fax: + 65 6779 1459. E-mail address: [email protected] (K.J. Chua) Keywords: Heat demand; Forecast; Climate change

1876-6102 © 2017 The Authors. Published by Elsevier Ltd.

Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the World Engineers Summit – Applied Energy Symposium & Forum: Low Carbon Cities & Urban Energy Joint Conference. 10.1016/j.egypro.2017.12.685

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1. Introduction In modern buildings, indoor air pollutants coming from building materials are of great concern. Volatile organic compounds (VOCs) is one of the major indoor airborne pollutants since some VOCs are related to the sick-building syndrome [1]. Cheng et al. [2] compared the characteristics of VOC emissions from several building materials. Sidheswaran et al. [3] proposed to purify the air by use the activated carbon fiber filters in the air-conditioning system. The design of air-conditioning mechanical ventilation (ACMV) system influences the building energy consumption and the indoor pollutant removal process [4]. Several researchers have proposed alternative cooling and ventilation strategies for reducing energy consumption as well as improving indoor air quality [5]. Rackes et al. [6] provides guidelines and performance labelling for buildings in tropical climates. Lee et al. [7] proposed a combined system by incorporating the dedicated outdoor air ventilation (DV) into the dry cooling (DC) air-conditioning system. The DCDV was demonstrated to achieve an annual energy saving by 54% over CAV system with reheat. Hughes et al. [8] investigated an energy recovery system for natural ventilation based on heat pipe technology. The system was able to reduce the energy consumption loads in domestic buildings. The conventional ACMV system usually relies on outdoor air ventilation to dilute and remove the indoor air contaminants. The outdoor air may sometimes contain high levels of pollutants. As a result, the conventional ventilation process using unhealthy outdoor air can deteriorate the indoor air quality. The present work aims to develop an air treatment system combining the air purification process, and investigate the energy saving potentials in tropical climate such as Singapore. 2. Description of the air treatment system Fig. 1 presents an overview of the schematic diagram of the proposed air treatment system (ATS). The proposed ATS consists of three sub-systems, namely, (i) energy-efficient oxygen production sub-system; (ii) ozone-based oxidation treatment sub-system; and (iii) air scrubbing sub-system. The detailed description of each component is provided as follows.

Fig. 1. Schematic of the air treatment system.



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The energy-efficient oxygen production process involves a combination of electrolysis, photocatalysis with the option of incorporating photovoltaic panels. It is able to provide oxygen by using renewable resources such as water and sunlight. The oxygen will be used for ozone generation and O 2-enrichment of the supply air. The ozone-based treatment process is an effective approach of cleaning indoor air. Volatile organic compounds (VOCs) are the toxic indoor pollutants. The ozone oxidation treatment can reduce the concentration of VOCs and convert VOCs into harmless substances. In addition, ozone is an excellent disinfectant to kill bacteria, viruses and odours. The air scrubbing sub-system comprises the activated carbon filter to reduce the concentration of CO 2 and further remove other unwanted air contaminants such as VOCs, dusts and smokes. In sum, three sub-systems constitute the entire picture of the proposed ATS. The return air is first purified through the ozone-based oxidation treatment process. Once the ozone concentration is high, the concentration of ozone can be reduced immediately to within safe level by using an ozone destructor. Thereafter, the air scrubber reduces the concentration of CO2 and further remove other unwanted air contaminants. Due to the air-purification and oxygen enrichment processes, the proposed ATS is able to employ a lower outdoor-air fraction resulting in marked savings on energy consumption of the air conditioning system. To investigate the energy performance of the proposed ATS and the thermal load in Singapore, a hypothetical office building was selected to conduct the calculation using the building energy simulation program “EnergyPlus” [9]. The total conditioning space area of the five-story office building is 3000 m2. The design values for occupancy, lighting load, and equipment load are 0.3 person/m2, 10.66 W/m2, and 7.64 W/m2, respectively. Singapore (located at 1°17′N, 103°50′E) has a typically tropical climate. The weather condition presents a small variation from month to month, with high temperature and humidity all year round. The design outdoor air dry bulb temperature is 33.2 °C. The average monthly relative humidity ranges from 81% to 89%. 3. Results and discussion 3.1. Influence of outdoor air intake on cooling load An hour-by-hour analysis on the cooling load has been conducted to investigate the cooling load profiles. The building energy simulation is performed by using the software EnergyPlus based on the weather conditions on a design day (21 June) in Singapore.

Fig. 2. Impact of outdoor air flow rate on the profiles of the total cooling load on design day.

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To determine the maximum cooling load, the design values of internal load are employed in the simulation throughout the design days. The outdoor air intake of 10 L/s per person is considered as a requirement for office spaces. However, during haze situations, reducing the outdoor air intake while switching on the proposed ATS would be an attractive method to provide improved indoor air quality. Fig. 2 presents the impact of outdoor air intake on the profiles of total cooling load for a period from 7 am to 7 pm on the design day. In tropical climate, the outdoor air enthalpy is usually high. Therefore, the cooling demand for conditioning the outdoor air constitutes a large portion of the total cooling load. It is observed that a reduced outdoor air intake results in a lower cooling load. For example, by decreasing the outdoor air intake from 10 L/s person to 5 L/s per person, the peak total cooling load decreases by 30.75%. In other words, a potential energy savings can be expected due to the reduction of outdoor air intake. 3.2. Monthly electricity peak demand for cooling The building energy consumption performance has been analysed for one year based on the climate data for Singapore. The monthly weather condition in Singapore is presented in Fig. 3. The average outdoor air dry bulb temperature and relative humidity show a small month-to-month variation. As shown in Fig. 3, December has the lowest average monthly temperature of 26.3 °C, and June has the highest average temperature of 28.5 °C.

Fig. 3. Profile of monthly weather condition in Singapore.

Fig. 4. Monthly electricity peak demand for cooling.



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Fig. 4 illustrates the profiles of monthly electricity peak demand for cooling with varying outdoor air flow rates. In tropical climates, the electricity demand for cooling dose not vary considerably from month to month. For the outdoor air supply of 10 L/s per person, the highest electricity demand for cooling occurs in June (44.5 W/m 2), and the lowest electricity demand appears in December (33.8 W/m2). In addition, the reduction of outdoor air flow rate is able to effectively decrease the electricity peak demand for cooling. For example, in January, 41% reduction in the electricity peak demand is achieved by changing the outdoor air flow rate from 10 L/s per person to 2 L/s per person. 3.3. Annual energy consumption The energy consumption in the building has been estimated for one year based on the climate date for Singapore. The annual energy consumption of key components is illustrated in Fig. 5. The ATS is activated once the outdoor air intake rate is less than 10 L/s per person. Comparing to the condition with an outdoor air intake rate of 10 L/s per person, the energy consumption for cooling is reduced by 23.4% for the outdoor air intake rate of 2 L/s per person.

Fig. 5. Annual energy consumption under varying outdoor air flow rate.

The energy saving potential can be attributed to the consequence of the decreased total cooling load. The ATS is able to attain an annual energy consumption saving of 40.56 kWh/ m2 by simply regulating the outdoor air intake from 10 to 2 L/s per person.

4. Conclusions The building simulation has been conducted by using EnergyPlus platform under Singapore climate. The proposed ATS enables a lower outdoor air intake rate while realizing improved indoor air quality. The potential energy savings can be expected due to the reduction of outdoor air intake. By regulating the outdoor air intake from 10 to 2 L/s per person, the ATS is able to achieve an annual energy consumption saving of 40.56 kWh/ m2.

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Acknowledgements The authors gratefully acknowledge the generous funding from the National Research Foundation (NRF) Singapore under the Energy Innovation Research Programme (EIRP) Funding Scheme (R-265-000-515-279) managed on behalf by Building and Construction Authority (BCA). References [1] Zhang LZ, Niu JL. Mass transfer of volatile organic compounds from painting material in a standard field and laboratory emission cell. International Journal of Heat and Mass Transfer 2003;46:2415–23. [2] Cheng Y-H, Lin C-C, Hsu S-C. Comparison of conventional and green building materials in respect of VOC emissions and ozone impact on secondary carbonyl emissions. Building and Environment 2015;87:274–82. [3] Sidheswaran MA, Destaillats H, Sullivan DP, Cohn S, Fisk WJ. Energy efficient indoor VOC air cleaning with activated carbon fiber (ACF) filters. Building and Environment 2012;47:357–67. [4] Cao G, Awbi H, Yao R, Fan Y, Sirén K, Kosonen R, et al. A review of the performance of different ventilation and airflow distribution systems in buildings. Building and Environment 2014;73:171–86. [5] Chua KJ, Chou SK, Yang WM, Yan J. Achieving better energy-efficient air conditioning – A review of technologies and strategies. Applied Energy 2013;104:87–104. [6] Rackes A, Melo AP, Lamberts R. Naturally comfortable and sustainable: Informed design guidance and performance labeling for passive commercial buildings in hot climates. Applied Energy 2016;174:256–74. [7] Lee WL, Chen H, Leung YC, Zhang Y. Decoupling dehumidification and cooling for energy saving and desirable space air conditions in hot and humid Hong Kong. Energy Conversion & Management 2012;53:230–9. [8] Hughes BR, Chaudhry HN, Calautit JK. Passive energy recovery from natural ventilation air streams. Applied Energy 2014;113:127–40. [9] Nguyen A-T, Reiter S, Rigo P. A review on simulation-based optimization methods applied to building performance analysis. Applied Energy 2014;113:1043–58.