Complexity in Designing Energy Efficient Buildings: Towards Understanding Decision Networks in Design

Most important decisions for designing energy efficient buildings are made in the early stages of design. Designing is a complex interdisciplinary task, and energy efficiency requirements are pushing boundaries even further. This study analyzes the level of complexity for energy efficient building design and possible remedies for managing or reducing the complexity. Methodologically, we used the design structure matrix for mapping the current design tasks and hierarchical decomposition of lifecycle analysis for visualizing the interdependency of the design tasks and design disciplines and how changes propagate throughout the system, tasks and disciplines. We have visualized the interdependency of design tasks and design disciplines and how changes propagate throughout the system. Current design of energy efficiency building is a linear and one-shot approach without iterations planned into the process. Broken management techniques do not help to reduce the complexit

Defining the Reference Hotel – toward nearly Zero Energy Hotels design

The ever mentioned “cost optimality” and “nearly Zero Energy Buildings” concepts, introduced by the EPBD recast, are still a blurry target at EU Member States’ level for non-residential buildings. Among the uncertainties hampering a quantitative description of cost optimal and nearly Zero Energy (nZE) level of energy performance in these building categories, the definition of the “typical energy use of a building” [1], is a key issue. Indeed, in non-residential buildings the energy use for maintaining occupants’ comfort (identified as the “typical”) is complementary to the energy use for maintaining the offered services’ quality. Given the general issue, the paper focuses on hotels. As an initial step toward nZE hotels, this study presents the definition of an existing Reference Hotel. First, typical and extra functions of a small-medium hotel were defined. Then, the general procedure for defining a Reference Hotel (RH) was drafted and an Italian RH was modelled: internal layout, envelope, systems features and operation profiles were identified. A dynamic energy simulation of the model was run to evaluate its energy performances. Results were then compared to benchmarks from literature. Next steps will exploit the Reference Hotel to investigate potential relations with the energy uses for extra services and to propose cost-optimal and energy efficient retrofit measures

New dose-response model and SARS-CoV-2 quanta emission rates for calculating the long-range airborne infection risk

Predictive models for airborne infection risk have been extensively used during the pandemic, but there is yet still no consensus on a common approach, which may create misinterpretation of results among public health experts and engineers designing building ventilation. In this study we applied the latest data on viral load, aerosol droplet sizes and removal mechanisms to improve the Wells Riley model by introducing the following novelties i) a new model to calculate the total volume of respiratory fluid exhaled per unit time ii) developing a novel viral dose-based generation rate model for dehydrated droplets after expiration iii) deriving a novel quanta-RNA relationship for various strains of SARS-CoV-2 iv) proposing a method to account for the incomplete mixing conditions. These new approaches considerably changed previous estimates and allowed to determine more accurate average quanta emission rates including omicron variant. These quanta values for the original strain of 0.13 and 3.8 quanta/h for breathing and speaking and the virus variant multipliers may be used for simple hand calculations of probability of infection or with developed model operating with six size ranges of aerosol droplets to calculate the effect of ventilation and other removal mechanisms. The model developed is made available as an open-source tool

Zonal modeling of air distribution impact on the long-range airborne transmission risk of SARS-CoV-2

A widely used analytical model to quantitatively assess airborne infection risk is the Wells-Riley model which is limited to complete air mixing in a single zone. However, this assumption tends not to be feasible (or reality) for many situations. This study aimed to extend the Wells-Riley model so that the infection risk can be calculated in spaces where complete mixing is not present. Some more advanced ventilation concepts create either two horizontally divided air zones in spaces as displacement ventilation or the space may be divided into two vertical zones by downward plane jet as in protective-zone ventilation systems. This is done by evaluating the time-dependent distribution of infectious quanta in each zone and by solving the coupled system of differential equations based on the zonal quanta concentrations. This model introduces a novel approach by estimating the interzonal mixing factor based on previous experimental data for three types of ventilation systems: incomplete mixing ventilation, displacement ventilation, and protective zone ventilation. The modeling approach is applied to a room with one infected and one susceptible person present. The results show that using the Wells-Riley model based on the assumption of completely air mixing may considerably overestimate or underestimate the long-range airborne infection risk in rooms where air distribution is different than complete mixing, such as displacement ventilation, protected zone ventilation, warm air supplied from the ceiling, etc. Therefore, in spaces with non-uniform air distribution, a zonal modeling approach should be preferred in analytical models compared to the conventional single-zone Wells-Riley models when assessing long-range airborne transmission risk of infectious respiratory diseases

Comparison of Simplified and Detailed Window Models in Energy Simulations

The purpose of this study is to quantify the gap between the calculated energy need of a building model with simplified and detailed windows and suggest a method for reducing the gap. We composed a model of a detached house in the cold climate of Estonia and studied its energy needs with triple and quadruple windows. Standard window models resulted in heating need lower by up to 7% and cooling need higher by up to 23%. In case of triple windows multiplying the U-value of standard window models by 1.15 minimized the mismatch in the calculated energy needs with different window models

Danish, Estonian and Finnish NZEB requirements comparison with European Commission recommendations for office buildings in Nordic and Oceanic climates

Direct comparison of building energy performance levels between countries is usually not possible due to differences in climatic conditions, calculation methods, primary energy (PE) factors and input data. The aim of this paper is to analyse the differences in nearly zero energy office buildings requirements and energy calculation methodology in Denmark, Finland, and Estonia. The study is based on a newly built Estonian office building, designed to meet national NZEB requirements. To account for the climatic differences between the countries a heating-degree-days-based correction factor was applied for building envelope thermal transmittance. NZEB requirements for each country are compared with European Commission (EC) recommended values (EU 2016/1318) using normalization and benchmarking through detailed computer simulations. National NZEB primary energy threshold was needed to be reduced by 7% in Denmark and by 23% in Estonia to meet EC recommendations. At the same time, the flagship reference building, that was better than Estonian NZEB, met both Nordic and Oceanic EC recommendations. Finnish NZEB requirement was not exceeded with any building configuration applied in this study, indicating that Finnish NZEB is considerably less strict compared to Danish and Estonian ones

Estimating the impact of indoor relative humidity on SARS-CoV-2 airborne transmission risk using a new modification of the Wells-Riley model

A novel modified version of the Wells-Riley model was used to estimate the impact of relative humidity (RH) on the removal of respiratory droplets containing the SARS-CoV-2 virus by deposition through gravitational settling and its inactivation by biological decay; the effect of RH on susceptibility to SARS-CoV-2 was not considered. These effects were compared with the removal achieved by increased ventilation rate with outdoor air. Modeling was performed assuming that the infected person talked continuously for 60 and 120 min. The results of modeling showed that the relative impact of RH on the infection risk depended on the ventilation rate and the size range of virus-laden droplets. A ventilation rate of 0.5 ACH, the change of RH between 20% and 53% was predicted to have a small effect on the infection risk, while at a ventilation rate of 6 ACH this change had nearly no effect. On the contrary, increasing the ventilation rate from 0.5 ACH to 6 ACH was predicted to decrease the infection risk by half which is remarkably larger effect compared with that predicted for RH. It is thus concluded that increasing the ventilation rate is more beneficial for reducing the airborne levels of SARS-CoV-2 than changing indoor RH. Practical implications: The present results show that humidification to moderate levels of 40%–60% RH should not be expected to provide a significant reduction in infection risk caused by SARS-CoV-2, hence installing and running humidifiers may not be an efficient solution to reduce the risk of COVID-19 disease in indoor spaces. The results do however confirm that ventilation has a key role in controlling SARS-CoV-2 virus concentration in the air providing considerably higher benefits. The modified model developed in the present work can be used by public health experts, engineers, and epidemiologists when selecting different measures to reduce the infection risk from SARS-CoV-2 indoors allowing informed decisions concerning indoor environmental control

Compliance with Summer Thermal Comfort Requirements in Apartment Buildings

In this study we have investigated the compliance with summer thermal comfort requirements of 16 new apartment buildings in Estonia by modelling and simulating dwellings using energy and indoor climate simulation software IDA-ICE. We also conducted field measurements of indoor temperature in 17 dwellings in 16 different apartment buildings during the period from 1 July to 31 August 2014. It has been found that 81.3% of the simulated buildings do not comply with the requirements. Measurements show that overheating can be a problem in apartment buildings also in cold climate regions