5.1
Methods introduction
This thesis primarily presents research from computer simulations and laboratory experiments. Thus, it differs from the traditional theses published at the Architecture faculty, where qualitative methods are more common. The work presented here is centred on quantitative descriptors used to assess the building performance as a function of window configurations. Some qualitative aspects have, however, been studied. These are related to the thermal and visual comfort of users of the studied office spaces. This chapter presents an overview of the tools used in the various parts of the thesis. A more detailed description of methods, experimental design and software is given in the respective papers.
5.2
Component-level analysis tools
5.2.1 THERM and WINDOW
THERM and WINDOW software have been the primary analysis tools of the component-level performance. THERM incorporates a two-dimensional heat transfer model, utilizing a finite element method to numerically solve the governing two- dimensional energy flow equations. The details of the models are given in [89].
The WINDOW program was used to assess the centre-of-glazing properties. Fenestration product heat transfer through the centre-of-glazing area is primarily a one- dimensional process. It is analysed by breaking down the glazing system cross section into an assembly of nodes and calculating the heat transfer between each node. WINDOW models the user-defined glazing system as a one-dimensional, steady-state resistance network. An iterative solution method is then used to converge upon the correct temperature distribution. From this temperature distribution, any desired performance index can be calculated.
To accurately model glazing systems with multiple spectrally selective glazings (e.g. glazings with solar-optical properties which vary by wavelength, such as many low- emissivity coatings), a multi-band model is used in WINDOW. In this model, WINDOW calculates the transmittance and reflectance for the glazing layer or the glazing system wavelength by wavelength and then weights the properties by the appropriate weighting functions to obtain the total solar, visible, thermal infrared properties. To use the multi-band model, WINDOW needs a spectral data file for each glazing layer. These data files are updated and maintained by Lawrence Berkeley National Laboratories (LBNL) and are available from the National Fenestration Rating Council (NFRC) [78]. If some of the glazing layers in a glazing system do not have a spectral data file, WINDOW assumes a flat spectral behaviour of the glazings without the spectral data files, based on their stated visible and solar properties [90].
5.3
Building-level analysis tools
5.3.1 SIMIEN
SIMIEN is a tool based on monthly stationary calculations. The algorithms used are described and validated against NS-EN 15265:2007 [70]. The calculations are based on hourly simulation data. SIMIEN was used for an introductory study in paper 1 of this thesis. This software was chosen because it has a well-developed and user-friendly graphical user interface (GUI), and it is a much-used tool among consultants and energy advisors/architects in the Norwegian building industry. However, it has some weaknesses in that there is no representation of the real geometry of buildings and an hourly time-step for calculations is used according to a simplified model in NS 3031 [69]. These issues affected the expected accuracy of the calculation results which led to the decision to switch to a more detailed tool for the remainder of the work. The choice fell on EnergyPlus.
5.3.2 EnergyPlus – BES modelling software
EnergyPlus is an integrated simulation tool. This means that all three of the major parts; building (building envelope), system and plant (zone and air distribution system), are solved simultaneously. The basis for the zone and air system integration is to formulate energy and moisture balances for the zone air and solve the resulting ordinary differential equations using a predictor-corrector approach. Conduction Transfer Functions (CTF) are used for building envelope calculations and are solved using state space methods [84]. The software is flexible and allows for a good representation of integrated simulations of building envelope and HVAC systems in combination. It also allows detailed input of building geometry. There are, however, some drawbacks. Several add-ons have been included since development which has led to a complex programming code and a resulting lack of traceability of the exact code and algorithms used.
EnergyPlus is a commonly used tool which has shown fair correspondence with other similar simulation tools like ESPr and TRNSYS [91]. Accuracy of the software has also been investigated in IEA ECBCS Annex 43 [92]. Simulated values for air temperatures, daylight illumination levels and heating demands were compared to measurements in test office cells with various shading devices and shading control strategies. Estimated values of air temperatures and airflow rates were in general within a 5 % error margin from the measured values. However, prediction of exterior daylight illuminance levels
must be aware of. It has reduced flexibility compared to EnergyPlus as it is only possible to do room-level studies. Choices for HVAC design, strategies and set points are set to default values that cannot be altered. It was, however, found to be suitable for some of the studies carried out in this work based on the beneficial aspects of this tool.
5.4
Laboratory measurements – description of equipment and
methods
A full-scale climate simulator, as shown in Figure 4 has been used to assess the thermal and optical performance of a dynamic translucent façade system. A hot box, shown in Figure 4, has been used to measure the thermal transmittance of windows with integrated solar shading devices.
The climate simulator introduces a new way of testing the performance of building components. Temperature controls are coupled with solar radiation stresses using xenon lamps to mimic the spectral distribution of real solar radiation. No governing standards are available for the description of procedures etc. for this apparatus. The climate simulator is described in more detail in paper 4.
Figure 4. Climate simulator (left), hot box (right).
Measurements in the hot box were carried out according to governing standard for window measurements, SO 12567-1:2010 Thermal performance of windows and doors
- Determination of thermal transmittance by the hot-box method - Part 1: Complete windows and doors [79]. A detailed description of the hot box, relevant measurement
standards, procedures and a supplementary discussion relating to estimation of uncertainties are presented in paper 5.