公共建筑能源效率与室内空气质量中英文2018原文Energy efficiency – indoor air quality dilemma in public buildingsLiva Asere, Andra BlumbergAbstractThe energy efficiency –indoor air quality dilemma is a common predicament in many buildings undergoing energy efficiency improvements. The main goal of this research is to study the impact of this dilemma on national final energy consumption and greenhouse gas emission reduction. A simulation using a system dynamics model was carried out. The stock of public buildings was split into four sub-categories based on when the buildings were constructed. Natural ventilation is used in all buildings before renovation. After implementing energy efficiency measures, two scenarios are simulated: one with and one without mechanical ventilation. Buildings constructed between 1940 and 1992 exhibit the greatest increase in both floor areas with energy efficiency measures and profitability ratio. The simulation results show that if ventilation is operated according to national building standards, total energy consumption in public buildings increases by 1.3 % in 2014 and by 2 % in 2040 compared to the situation where there is no mechanical ventilation. If the implementation of the energy efficiency measures is increasing at higher rate, the difference between bothalternatives is increasing more. Energy efficiency measures in public buildings reduce national energy consumption and greenhouse gas emissions. However these measures also reduce indoor air quality thereby causing losses of productivity of the building occupants.Keywords：energy efficiency，government，municipalities，public building，system dynamics modelling，energy savings，CO2 emissions1. Introduction and background informationThe majority of building stock in Latvia was built during the period when energy efficiency was not a priority. For the most part, these buildings do not offer the comfort and the quality of life expected today by the people who work and live in them. Due to climate change concerns, improving the energy efficiency of these buildings is a priority of the national energy policy. Energy consumption of public buildings, including both municipal and state-owned buildings represents a substantial part of Latvia’s total energy consumption. To increase energy efficiency in public buildings, EU directive 2012/27/EU on energy efficiency [1] has set a specific goal for member countries: 3 % of the total floor area of heated and/or cooled buildings owned and occupied by central governments are to be renovated each year to meet 2014 minimum energy performance standards. The same directive requires that member states set a national energy consumption and efficiency target. Improvingthe energy efficiency of publicly-owned buildings is therefore critical to achieving the national energy efficiency goals. To reach these goals, substantial improvement measures have to be implemented in the existing public building stock.Current building standards provide that building envelopes be highly air tight. This leads to the energy efficiency/indoor air quality dilemma. In spaces with high occupant density, e.g. in schools, conference rooms, offices, etc. where CO2 and VOCs are the main indoor pollutants, air tight building envelopes are to a high degree responsible for unacceptable indoor air quality. To improve indoor air quality in buildings where adequate natural ventilation is not available, mechanical ventilation systems have to be used. Such systems increase energy consumption leading one to assume that indoor air quality and thermal comfort/worker or human productivity are not consistent with energy efficiency. Studies show that the poorer the indoor air quality, the lower the human productivity (a 15 % reduction in performance of schoolwork corresponds to about 1 year of teaching [2]). Excess CO2 (more than 1000 ppm) and VOCs levels in indoor air lead to acute health effects such as irritation of eyes and respiratory tract, headaches, dizziness, loss of coordination, nausea, visual disorders, and allergic reactions, including asthma and rhinitis. Higher levels of VOCs can have chronic adverse health effects such as damage to liver, kidney, blood system and central nervoussystems (CNS). Some VOCs, e.g. formaldehyde, may even cause cancer in humans [3]. A review of international scientific literature shows that this dilemma occurs widely, however, there is as yet no specific solution to the problem.Studies carried out in Latvia [4, 5] show that the operation of ventilation systems does not produce the required indoor air quality and thermal comfort, and the operation of ventilation systems can make it difficult or impossible to achieve the planned energy efficiency goals. The measured CO2 level in these cases was between 1000 ppm and 2500 ppm. One study also included a detailed assessment of the effect of the dilemma on human productivity. Results of this study show that an improvement in indoor air quality will generate a 19 % increase in productivity. But improving the air quality using mechanical ventilation systems also requires additional energy consumption, which in turn, lowers the energy efficiency in buildings. The findings in Latvia coincides with studies in other countries, e.g. the measured CO2 in schools:In UK is 2100–5000 ppm;In Denmark 500–1500 ppm;In Poland 1000–4200 ppm;In Sweden 425–2800 ppm;In the Netherlands 900–2100 ppm;In USA 300–5000 ppm.Thus the ventilation rate is only 1 l/s/person [2] while the standards and/or norms require 4.8–14 l/s per person depending on the category (quality class) and type of building material used [6].The main goal of this research is to assess the impact of the energy efficiency/indoor air quality dilemma for public buildings on both national energy consumption and greenhouse gas emission reduction. A simulation with system dynamics model was used.2. MethodologySystem dynamics is a mathematical modelling technique, which is used to solve complex dynamic problems in non-linear systems driven by feedbacks. This method is based on the study of the structure of the system and behavior generated by this structure [7]. The structure is made up of stocks where accumulation occurs and flows, changing the state of the stocks.A previously-developed system dynamics model of energy efficiency improvements in public buildings [8] is used for this study. The structure of the model is adjusted by splitting the total stock of public building into four sub-models based on construction periods (Fig. 1). The first sub- model includes historic buildings built before 1940. Most of these buildings have heritage value and a limited set of energy efficiency measures can be employed. For example, as external insulation is notacceptable, internal insulation would have to be used. Buildings in the second sub-model are those built between 1940 and 1992. These have been constructed according to the building standards of the former Soviet Union. The third sub-model comprises buildings constructed between 1992 and 2014. During this period, energy efficiency standards have changed twice, each time getting more stringent. The last sub-model includes buildings built after 2014: current building standards require that these be low energy buildings [9].Input data for each of the sub-models are presented in Table 1. They are used as initial data for simulation. Data for heated areas are obtained from the Long-term building renovation strategy [10]. Insulation costs and energy consumption were collected from the database of implemented energy efficiency projects [11]. The simulation period is from 2014 to 2040.Initial values used for the main general variables are:Capacity of building companies is 35000 m2/year;Heating tariff is 58 MWh/year;Electricity tariff 140 EUR/MWh;Tariff increases of 2 % per year;EU funds and public funding for state-owned buildings: o from 2016 to 2019 is 97.2 million EUR, from 2018 to 2022 is 38.2 million EUR;Annual public funding for municipal buildings:0.5 million EUR in 2014,1.5 million EUR starting from 2015;Every year new buildings are built at the rate of 3 %.Profitability also influences the way the model functions: the higher the potential profitability, the higher the share of funding allocated to that building group. Funding is allocated to different building sub-models based on the profitability ratio in the following way.It is assumed that only natural ventilation with an air exchange rate of 0.7 h–1 had been installed and operated before the addition or implementation of energy efficiency measures. An average air exchange rate of 4 h–1 created by mechanical ventilation is used for the simulation after the implemen tation of energy efficiency measures. For Latvia’s climate, the specific energy consumption after implementation of energy efficiency measures is 9 kWh/m2/year for heating supply air and 4 kWh/m2/year for electricity with a heat recovery efficiency of 80 % and specific fan power of 1.25 kW/(m3/s) operating for 12 hours during working days.3. Results and discussionFig. 2 shows total energy consumption in public buildings both with and without the operation of mechanical ventilation systems. In both cases total energy consumption decreases. At the beginning the difference between both alternatives is 1.3 % and increases by time and it reaches2 % by 2040 or CO2 emissions 7050 t/year. By 2040 in 667 thousand m2 energy efficiency measures will be carried out, and this represents only 10 % of the total floor area of those buildings built before 2014. If energy efficiency measures are implemented at higher rate, the difference in energy consumption between two alternatives increases by 2040.The difference in the growth rate of building floor area with energy efficiency measures is explained by the profitability ratio –the highest ratio is for buildings built from 1940 to 1992 as they have the highest energy efficiency potential, followed by the historic building stock, which have lower energy efficiency potential due to technical limitations and heritage value. The lowest profitability ratio is for buildings built between 1993 and 2014. They have the lowest energy saving potential compared to costs of construction.Profitability ratio presented in Fig. 4 shows dynamic behaviour over time. Changes are caused by feedbacks, non-linearity and delays built within the system. Supply and demand of energy efficiency measures are illustrated in Fig. 5. When no funding is available, demand and supply of energy efficiency measures is low and prices are low as well. As soon as funding enters the market, demand rises as does supply. However, it takes time to build up the capacity of construction companies. In these circumstances prices rapidly increase due to the gap between supply and demand. When supply and demand are in equilibrium, prices start to fall.When funding is removed, demand falls, followed by supply and in short order prices fall as well. This process where large amounts of funding suddenly flow into the market causes a decrease in profitability as can be seen, and fewer buildings can be renovated due to very high prices compared to conditions before funding.4 ConclusionsSimulation with a system dynamics model revealed that the implementation of energy efficiency measures in public buildings has a major impact on indoor air quality, leading to an energy efficiency/indoor air quality dilemma. On the one hand, energy efficiency measures in public buildings reduce both national energy consumption and greenhouse gas emissions, but on the other hand they reduce indoor air quality thus causing losses in productivity for building occupants. If mechanical ventilation is used, indoor air quality is improved and productivity is increased but this comes with increased energy consumption. The simulation results show that if ventilation is operated according to national building standards, total energy consumption in public buildings increases by 1.3 % in 2014 and by 2 % in 2040 (or CO2 emissions 7050 t/year) compared to the situation where there is no mechanical ventilation. If the implementation of the energy efficiency measures is increasing at higher rate, the difference between both alternatives is increasing more. In schools the key goal of education isimproving individual outcomes as Hayward, Hunt and Lord [12] have emphasized in their research. The priority should be buildings that achieve sustainable development and yet meet the needs of the present without compromising the ability of future generations to meet their own needs.In addition to providing an assessment of the energy efficiency/indoor air quality dilemma, the model also provides insights into how energy efficiency is affected by supply and demand. The structure of the model reveals how the behaviour of the system is changed by feedbacks, non-linearity and delays built into the system. Failure in the timely disbursement of public funding leads to higher construction prices, which in turn leads to fewer buildings being constructed that implement energy efficiency measures for the same amount of money.译文能源效率–公共建筑中的室内空气质量困境摘要能源效率–室内空气质量困境是许多正在进行能源效率改善的建筑物所普遍面临的困境。