Effects of Fixed and Motorized Window Louvers on the Daylighting and Thermal Performance of Open-Plan Office Buildings

This study investigates the daylighting and thermal performance of open-plan office buildings with two scenarios of daylight louvers – fixed and motorized ones. Both types are for facade window applications. They redirect transmitted daylight to eliminate glare on occupants and increase daylight levels deeper in the interior space, but have significantly different daylight transmitting characteristics. In addition to daylighting, these louvers also affect solar heat gain. The tilt angle of slats in motorized louvers can be adjusted to control solar heat gain and daylight. In this study, an existing energy-efficient office building with fixed louvers is used. A combined thermal and daylighting model for a typical section of the building is developed using a simplified approach, and validated with measured data. The option of motorized louvers is then added to this model. The daylighting and thermal performance for different designs and seasons are assessed using the model. Results show that motorized louvers can effectively enhance useful solar heat gain and/or daylighting. The effect of building depth is also investigated

Impact of an Energy Efficiency Regulation in Northern Canada

Extreme cold climates and Canada’s sparsely populated Northern regions have limited human and infrastructural capacity making it difficult to build energy-efficient homes. Despite such differences, homes are built based on codes and standards developed for Canada’s South. In 2008, a by-law was passed in Yellowknife, Canada requiring a minimum EnerGuide Housing (EGH) rating of 80 for all new single-family and two-family residential buildings. The EnerGuide’s Energy Rating Service (ERS) program is an energy assessment program for residential housing formerly known as the EnerGuide Rating for Houses (EGH). Homes are rated between 0 to 100; lower numbers represent homes that are less efficient and 100 represents an airtight and well-insulated house that is net-zero energy. 1002 homes from the City of Yellowknife evaluated since 1950s were studied from the ERS database, Performance metrics studied include energy intensity, EGH rating, ACH rating, window types, the thermal resistance of the building envelope, primary heating and hot water heating equipment’s efficiencies, total electricity used, and total energy used. The analysis identified the current state of housing in Yellowknife, past and present housing trends, and determined the effect of the city of Yellowknife’s new building by-law had on housing performance. The preliminary finding shows a pathway to significantly improve the energy efficiency of the housing stock in Yellowknife. This regulation shows other municipalities in Canada that legislations pushing energy efficient buildings can be very effective

Comparison Of Three Transient Models For Slab Heating/Cooling Systems

Radiant floor heating and cooling systems can be beneficial in various applications such as heating or cooling buildings and in infrastructure applications such as de-icing of bridges and roads as well as snow melting. Such systems usually include a significant amount of thermal mass, thus providing energy flexibility in buildings. Models of embedded-tube radiant systems are therefore useful to predict their behavior (rate of heat transfer and outlet heat-transfer fluid temperature), which can be used for the development of predictive control strategies and optimal control algorithms. As a result, a comparison of different models is conducted in this paper. The TRNSYS simulation software provides three different ways of modeling radiant floor systems (Type 56, Type 653, and Type 993), which are compared in this paper with one another in order to assess their accuracy and limitations. Each approach is compared with measurements from an experimental set-up in a controlled environmental chamber. This paper aims at: (i) evaluating the appropriate model resolution for embedded-tube radiant floor systems, (ii) validating experimentally the three aforementioned TRNSYS types (which have been validated qualitatively only), and (iii) providing a mathematical explanation of Type 993 (whose description is still unavailable to TRNSYS users). A sensitivity analysis is also performed to estimate the impact of the different types’ parameters

A Study of the Effect of Zone Design Parameters on Frequency Domain Transfer Functions for Radiant and Convective Systems

This paper presents a parametric study on the effect of a number of room design parameters for radiant and convective heating sources as well as solar gains. This study is performed using frequency domain modeling approach by means of which important room transfer functions are obtained and studied. Frequency domain modeling is a useful tool for analyzing building thermal dynamics as well as different design options. The phenomena affecting energy consumption inside a building such as solar gains, exterior temperature and heating/cooling sources are usually cyclic phenomena and can be modeled by means of frequency domain techniques assuming periodic conditions in the calculations. Using frequency domain techniques, the transient heat conduction inside the walls can be accurately modeled with no discretization for the thermal mass. However, there is difficulty modeling time-varying variables in the frequency domain. This is especially important in the case of convective and radiative heat transfer coefficients which are inherently non-linear elements. The coefficients are usually linearized in order to have a linear system of equation that can be presented by means of a linear thermal network[1]. In frequency domain modeling approach usually a constant value for the convective and radiative heat transfer coefficients is assumed. However, this assumption can produce significant errors when there are large differences between surfaces temperatures for example in the case of floor heating or direct gain rooms with large windows[2]. In this case, a sensitivity analysis on the magnitude of the important room transfer functions considering different values for convective and radiative heat transfer coefficients needs to be done. A room is considered with different types of heating (convective and radiative heating sources) and different levels of thermal mass on the floor. The effect of thermal mass and floor covering on the room thermal response considering different types of heating is investigated. Magnitude of the transfer functions between room air temperature and the convective heating source is a determining element in the room air temperature fluctuations considering thermal comfort aspects. Also, in the case of radiant heating, the transfer function between room air temperature and radiant heat source can be used to determine the room air temperature swings due to the floor radiant heating source. The sensitivity of the magnitude of the transfer functions versus different values of convective and radiative heat transfer coefficients is studied and compared. This study will guide future model predictive control (MPC) research by means of frequency domain techniques to make choices such as optimal thermal mass thickness for floor heating versus convective systems. It will contribute to linking design with MPC. [1] Athienitis, A.K. and O\u27Brien, W., Eds. (2015). Modelling, design and optimization of net-zero energy buildings, Solar heating and cooling, Berlin: Ernst, Wilhelm & Sohn 2015. [2] Saberi Derakhtenjani, Ali, Candanedo, Jos A., Chen, Yuxiang, Dehkordi, Vahid R., Athienitis, Andreas K. (2015), Modeling approaches for the characterization of building thermal dynamics and model-based control: a case study. ASHRAE STBE (Science and Technology for the Built Environment) Journal (21): 824-836

A Study of Temperature Set Point Strategies for Peak Power Reduction in Residential Buildings

AbstractThis paper presents an experimental and theoretical study of the dynamic response of residential buildings with different levels of thermal mass and their respective space heating peak demands for different room temperature set point profiles. Experiments were conducted at two identical and highly instrumented houses. One of them is modified with different floor coverings, while the other one is kept unchanged and used for reference. Their dynamic response to a night time setback set point profile with step changes is monitored and analyzed. Equivalent RC network thermal models are developed for a north zone of the houses. These models are then used to study the impact of set point ramping lengths and “near-optimal” transition curves between two temperatures on the peak demand reductions, while maintaining thermal comfort. It was found that, while taking into consideration the thermal response of the building due to the level of mass, an appropriate yet simple set point strategy to reduce peak electricity demand can be established. For a room with wood flooring, by replacing the conventional night time setback temperature profile with a one hour or two hour ramp, peak demand reductions of up to 10% and 25% can be achieved, respectively

Control-oriented Modelling of Thermal Zones in a House: a Multi-level Approach

This paper presents a multi-level approach to the problem of modelling different thermal zones in a house for control applications. This problem has been treated before by modelling the whole house with a single, all-inclusive RC circuit which may have different levels of resolution. The core of the proposed methodology lies in the possibility of allowing the user to switch back and forth between models representing different control levels according to the modelling objectives. For the development of specific control algorithms for each zone, the house can be treated as a collection of interconnected zonal models, as opposed to a single, large model. This modelling approach has the advantage of maintaining a simple structure for each zone, while also taking into account the heat transfer between zones; at this control level, issues such as occupancy, thermal comfort or setpoint profiles can be examined in detail. On the other hand, if the user is interested in a quick estimate of global variables (e.g., overall thermal load over the next 24 h) then different zones or even the entire house may be combined into a single low-order model. In summary, this multi-level approach allows the user to “zoom in and out†so that models at each control level remain manageable, easy to calibrate and easy to physically interpret. This paper uses data from an existing unoccupied test house, representative of a typical family home in Québec, as a case study. Four zones are considered: basement, main floor, upper floor and the attached garage. For the most detailed analysis, these zones are modelled with four interconnected zone models. Alternative ways of combining zones are investigated. A global low-order house model is used to calculate the thermal load of the building. Results of thermal load calculations are compared and discussed

Thermal performance of a hybrid BIPV-PCM: modeling, design and experimental investigation

In this paper, a BIPV-PCM installed in an office building façade is investigated to approach the practical application of PV-PCM. Based on an updated mathematical model, theoretical simulation has been conducted for BIPV-PCM in this case. Furthermore, field testing for this case has also been performed to validate the model, and then the simulated and experimental results are compared and found in considerably good agreement. The experiments have been conducted during the winter time, as the prototype has been installed in January 2013. The experimental and numerical results show a good agreement, the maximum electrical efficiency of this BIPV-PCM can reach 10% and the thermal one 12%

Estimating time constants for over 10,000 residential buildings in North America: towards a statistical characterization of thermal dynamics

Understanding the dynamic response of a building is essential in the design of sustainable energy-efficient buildings. Using data from over 10,000 smart thermostats, this study identifies patterns in the dynamic thermal response of residential buildings in Canada and the United States (US). The data set consists of one year of measurements recorded at 5-minute intervals for the indoor and outdoor air temperature as well as HVAC equipment run times. This study focuses on identifying effective values of time constants for the houses by applying the following procedure. First, periods complying with the following basic criteria are identified: a) the house is under free-floating conditions (i.e. when the HVAC system is switched off) for more than three hours and b) the outdoor temperature remains approximately constant (the outdoor temperature change is smaller than or equal to 2°C). Second, for each identified period, time constant values are determined by tracking the temperature responses of the house. These values are determined assuming the characteristic exponential decay of a first-order resistance-capacitance (RC) thermal model. Finally, a statistical analysis is applied to identify a typical range of effective time constant values according to month. Consequently, calculations show significant differences between estimated values for the summer and winter months, which may be attributed to occupant behaviour. In winter, the majority of time constants range from 15 to 55 hours. In summer, most of time constants vary between less than 1 hour and 18 hours due to occupants opening windows. In addition, the dependence of the time constant on the age of the home is investigated