Demand Controlled Ventilation

Transcription

1 Demand Controlled Ventilation Saving energy, improving economy and protecting the environment with Fläkt Woods Group Saving Energy, Economy and Environment with Fläkt Woods.

2 Introduction Today, most people spend over 90 percent of their time indoors e.g. at home, in schools, at hospitals and offices. Breathing fresh indoor air is vital for our health, performance and weel being, and could in fact be considered as a basic human right (1). However, we also know that providing the necessary amount of fresh air to create a comfortable and healthy indoor climate consumes energy in terms of electrical fan power as well as coolingand heating energy. Energy that, when produced also has a negative impact on our environment and contributes to the CO 2 -emissions to our atmosphere. In fact, approximately 40 percent of all the energy consumed in the European Union is used for buildings where ventilation and air conditioning are major contributors. As a consequence, and with the objective to reduce the CO 2 emissions with 20 percent until year 2010 (compared with 1996 levels), the Commission of the European Union have issued the Energy Performance in Buildings Directive (2002/91/EC). The directive is very clear on the fact that energy savings in buildings should not negatively affect the indoor climate conditions.

3 Article 1 Objective The objective of this Directive is to promote the improvement of the energy performance of buildings within the Community, taking into account outdoor climatic and local conditions, as well as indoor climate requirements and cost-effectiveness. Article 4 Setting of energy performance requirements 1. Member States shall take the necessary measures to ensure that minimum energy performance requirements for buildings are set, based on the methodology referred to in Article 3. When setting requirements, Member States may differentiate between new and existing buildings and different categories of buildings. These requirements shall take account of general indoor climate conditions, in order to avoid possible negative effects such as inadequate ventilation, as well as local conditions and the designated function and the age of the building. These requirements shall be reviewed at regular intervals which should not be longer than five years and, if necessary, updated in order to reflect technical progress in the building sector. Source: EPBD 2002/91/EC The indoor air directly affects people in all stages of life. Childrens performance and learning capabilities in classrooms, patients recovery from illness when in hospitals, peoples productivity and quality of work when in offices are all examples where international research have shown that indoor air quality (IAQ) has a critical impact on the outcome. In recent years, research has also shown a relation between inadequate ventilation and absence due to sickness emphasizing the importance of providing a healthy indoor air climate. The expression indoor air quality has different meanings depending on context. In this text, the following aspects of Air Quality are considered: Physical factors such as temperature and humidity. Mechanical factors such as air velocity and ventilation rate. Human bioeffluents (e.g, odours). So, is a healthy indoor air climate contradictory to a high level of energy performance in a building? No, the solution is Fläkt Woods Groups ventilation strategy based on Demand Controlled Ventilation!

4 Saving Energy and Protecting the Environment with Demand Controlled Ventilation What is Fläkt Woods Group Demand Controlled Ventilation? It is a ventilation strategy for a system where the air flow to specific spaces in a building are individually and dynamically regulated to actual demand and requirements. T he main objective of a Demand Controlled Ventilation system is to create a high level of indoor air quality and at the same time avoid unneccessary ventilation and thereby to save energy. Experience and field studies have shown that the level of CO 2 in a room is a reliable indicator of the air quality and ventilation rate, and could therefore be used as the determing parameter in Demand Controlled Ventilation systems. People are the main source of CO 2 in a building, if the number of people in a room are doubled, the CO 2 level will also double. If one, or a few people leave a room, the level of CO 2 will proportionally decrease. A high level of CO 2 in a rooom (>1000ppm) indicates that the ventilation rate is insufficient to obtain an adequate indoor quality. Consequently a low level of CO 2 (<600ppm) indicates that the ventilation rate could be turned down and thereby maintain a sufficient indoor air quality with lower energy costs. Large variations in ventilation requirements The usage pattern, and consequently the ventilation requirements of room can vary largely depending on several parameters, e.g. type of building, activities and purpose of the room, climatic (outdoors) conditions and time of the day. Just think of a classroom in a school where the occupancy pattern during a normal week changes from empty to 30 people several times every day. Here, it is obvious that a constant ventilation rate based on the requirement for a full room will lead to waste of energy when the room is empty, or when only a few people are in the room. Occupancy rates and energy savings An illustrating example of the variation in occupancy rates was presented 2005 in a doctoral thesis by Dennis Johansson (2). Here, results from field studies of three different buildings showed that the average occupancy rate varied between 35 and 55 % during normal office hours. The diagram shows that different spaces in the studied buildings are used to a different extent, but also that none of the room are used even close to 100 %. Assuming that the ventilation system was designed according to peak load with a static, constant air volume system (CAV), potential savings

5 from Demand Controlled Ventilation would be %. In general, Demand Controlled Ventilation systems are more advantageous in rooms that are subject to large variations or intermittent occupancy, but also rooms with static occupancy patterns will benefit from the adequate ventilation provided with this concept. Example 2 Occupancy rates for different spaces in three different buildings Occupancy rate / % MPO1 MPO2 MPO3 MPO4 MPO5 (Dennis Johansson 2005) MPO6 MPO7 MPO8 MPO Av UD1 UD2 UD3 UD4 UD5 UD6 UD7 UD Av IO Av Tot av Difference in occupancy between all-time and daytime Occupancy all-time

6 Improving Economy with Demand Controlled Ventilation Indoor air quality has financial impact in the areas of peoples well-being and thereby costs for sick leaves and health care. A study published 2007 by Middlesex University (3) shows the correlation between levels of CO 2 and well being of occupants. The most important findings from this study was the fact that when levels of CO 2 rise, the health complaints, tiredness and lack of concentration also rise. With CO 2 levels above 1500ppm, 79 % of the occupants reported feeling tired, and above 2000ppm 65 % of the occupants reported having no level of concentration. Even if it is difficult to set absolute figures on the economical impact, the conclusion is undoubtedly that poor indoor air qualtity will have impacy costs through sick leaves and decerased productivity and quality. Depending on how a building is used, the negative effects such as tiredness might even involve critical risks e.g. in surgical rooms, nuclear- or military control rooms etc. Unsatisfied tenants could also lead to increased costs for a building owner in terms of additional administration, bad-will and ultimately loss of income if the tenants decide to leave the buidling because of inadequate indoor climate conditions. Since CO 2 levels in a room can be considered proportional to the ventilation rate, it is also interesting to study the relationship between ventilation rates and sick leaves. Example 4 shows the compiled results of several studies and suggests that sick leaves will decrease when the ventilation rate increases. Example 3 & 4 The correlation between CO 2 (ppm) level and perceived tiredness 3. Relative sick-leave as a function of ventilation rate 30 Count of Level of tiredness during AM occupancy of room (blank) (Julie J Bennet 2007) Illness or sick leave prevalence relative to prevalence with no ventilation 1,0 0,8 0,6 0,4 0, X Ventilation rate (h -1 ) air changes per hour (Fisk et al. 2003) Alert and Awake Average No Level Tired, ocassional Yarning Very Tired (blank) X Drinka (1996), illness in nursing home Brundage (1988), illness in barracks, all years Particle concentration model Brundage (1988), illness in barracks, 1983 data Milton (2000), sick leave in offices

7 Indoor climate conditions, and its impact on human productivity Human performance is highly affected by the thermal conditions and perceived level of comfort. A study by Bjarne Olsen from International Center for Indoor Environ- ment and Energy (ICIEE) in Denmark, indicated that improved thermal com- fort, reduction in indoor pollutants, and enhanced ventilation rates and effectiveness can increase productivity by 5 to 10 percent. Conversely, the research also indicates that a 10 percent decrease in tenant satisfaction with IAQ results in a 1 percent drop in productivity In Finland, researcher Olli Seppanen, from the Helsinki University of Technology, developed a conceptual model to estimate cost effectiveness based on improved indoor environment. The model shows a decrease in performance by 2 percent for each degree increase of space temperature between 25 degrees C and 32 degrees C. Optimal productivity performance was found to occur when the space temperature was 22 degrees C. In a study conducted by Allan Hedge of Cornell University, low temperatures in work space also have a negative impact on productivity. His findings show that chilly workers not only make more errors, but cooler space temperature could increase the hourly labor cost by 10 percent. Fläkt Woods conclusion from these findings is that investing in a demand controlled ventilations system with individual temperature settings in every room will not only improve peoples well being and performance, but also reduce costs for sick leaves. References (1) Under the principle of human right to health, everyone has the right to breathe healthy indoor air. EUR/00/ World Health Organization (2) Modelling life cycle cost for indoor climate systems Report TVBH-1014 Lund Building Physics LTH. Dennis Johansson (3) Carbon Dioxide and IAQ Correlation, Julie J Bennet, M Middlesex University Bjarne W. Olsen (4), Indoor Environment Health, Comfort and Productivity, Clima 2005 Lausanne, 8th REHVA World Congress, Switzerland, Oct. 9-12, Olli Seppanen and William Fisk (5), A Method to Estimate The Cost Effectiveness of Indoor Environments in Office Work, Clima 2005 Lausanne, 8th REHVA World Congress, Switzerland, Oct. 9-12, 2005 Alan Hedge (6), Linking Environmental Conditions to Productivity, Eastern Ergonomics Conference & Exposition, New York, June 2004.

8 We Bring Air to Life FWG-DCV Brochure-EN Copyright 2008 Fläkt Woods Group Condesign Communications AB FläktWoods is a global leader in air management. We specialise in the design and manufacture of a wide range of air climate and air movement solutions. And our collective experience is unrivalled. Our constant aim is to provide systems that precisely deliver required function and performance, as well as maximise energy efficiency. Solutions for all your air climate and air movement needs FläktWoods is providing solutions for ventilation and air climate for buildings as well as fan solutions for Industry and Infrastructure. Air Handling Units (AHUs) Modular, compact and small AHU units. Designed to ensure optimisation of indoor air quality, operational performance and service life. Air Terminal Devices and Ducts Supply and exhaust diffusers and valves for installation onwalls, ceiling or floor are all included in our large range and fit all types of applications. Chilled Beams Active induction beams for ventilation, cooling and heating, and passive convection beams for cooling. For suspended or flush-mounted ceiling installation and multi-service configuration. With unique Comfort Control and Flow Pattern Control features. Residential ventilation A complete range of products for residential ventilation. Consists of ventilation units, exhaust air fans and cooker hoods designed to optimise indoor comfort and save energy. Energy recovery Dessicant-based product and systems that recover energy, increase ventilation and control humidity. Fans Advanced axial, centrifugal and boxed fans for general and specialist applications. Comprehensive range including high temperature and ATEX compliant options. Engineered for energy efficiency and minimised life cycle cost. Chillers Air-cooled and water-cooled chillers with cooling capacity up to 1800kW. Designed to minimised annual energy consumption in all types of buildings. Controls and drives Variable speed drives and control systems, all tested to ensure total compatibility with our products. Specialist team can advise on energy saving and overall system integration. Acoustical products A complete line of sound attenuating products, including rectangular and round silencers. Media Free silencers, custom silencers and acoustic enclosure panels. Fläkt Woods Group SA 18, avenue Louis Casaï, CH-1209 Geneva, Switzerland Tel info@flaktwoods.com See global website for international sales offices