Juha Jokisalo

Influence of energy demand response actions on thermal comfort and energy cost in electrically heated residential houses

This study has two aims to investigate the energy demand response (DR) actions on thermal comfort and energy cost in detached residential houses (1960, 2010 and passive) in a cold climate. The first one is to find out the acceptable range of indoor air and operative temperatures complying with the recommended thermal comfort categories in accordance with the EN 15251 standard. The second one is to minimize the energy cost of electric heating system by means of the DR control strategy, without sacrificing thermal comfort of the occupants. This research was carried out with the validated dynamic building simulation tool IDA Indoor Climate and Energy. Three different control strategies were studied: A) a strategy based on real-time hourly electricity price, B) new DR control strategy based on previous hourly electricity prices and C) new predictive DR control strategy based on future hourly electricity prices. The results show that the lowest acceptable indoor air and operative temperatures can be reduced to 19.4℃ and 19.6℃, respectively. The maximum annual saving in total energy cost is about 10% by using the control algorithm C.

Hourly test reference weather data in the changing climate of Finland for building energy simulations

Dynamic building energy simulations need hourly weather data as input. The same high temporal resolution is required for assessments of future heating and cooling energy demand. The data presented in this article concern current typical values and estimated future changes in outdoor air temperature, wind speed, relative humidity and global, diffuse and normal solar radiation components. Simulated annual and seasonal delivered energy consumptions for heating of spaces, heating of ventilation supply air and cooling of spaces in the current and future climatic conditions are also presented for an example house, with district heating and a mechanical space cooling system. We provide details on how the synthetic future weather files were created and utilised as input data for dynamic building energy simulations by the IDA Indoor Climate and Energy program and also for calculations of heating and cooling degree-day sums. The information supplied here is related to the research article titled “Energy demand for the heating and cooling of residential houses in Finland in a changing climate” [1].

Airtightness, Air Exchange and Energy Performance in Historic Residential Buildings with Different Structures

Abstract Old buildings that represent and maintain historic values often have poor indoor conditions and energy efficiency. The aim of this work was to evaluate the influence of building structures on airtightness and energy performance of certain historic building types. In this study on-site measurements, dynamic simulation and questionnaires were used. Significant differences between the levels of the airtightness of the historic houses exist in the studied region. No statistically significant correlation was found between the structure types and the envelope tightness. The typical air leakage places of the studied houses were at the junctions of the envelope structures. Measured air exchange rates indicated that the level of ventilation is insufficient in some of the houses while some are too leaky. If the airtightness of the naturally ventilated house is improved, the acceptable ventilation rate has to be guaranteed. Tightening the envelope and moving from natural to mechanical ventilation was the most effective way to improve the indoor conditions and energy performance.

A User-centric Demand Response Framework for Residential Heating, Ventilation, and Air-conditioning Load Management

Abstract The domestic heating, ventilation, and air-conditioning load promises a good prospect for electrical aggregators to consider it for demand response. This article presents a user-centric demand response control for scheduling the electric space heating load under a price and load uncertainty environment. The objective of the framework is to minimize a weighted sum of the expected payment, loss of comfort, and financial risk of a customer while strictly considering the end-user preferences. The household thermal behavior is modeled via an accurate two-capacity building model. The price and load uncertainty is modeled using a scenario-based stochastic programming approach. The proposed decision model is formulated as a non-linear programming problem that can be simply solved via commercially available solvers. The effectiveness of the formulation is demonstrated by applying it to a typical customer. The simulation results demonstrate that the decision mechanism allows consumers to compromise among electricity payment, thermal comfort, and risk exposure based on their thermal comfort preferences and risk priorities.

The use of displacement and zoning ventilation in a multipurpose arena

ABSTRACT This study investigated the performance of ventilation and indoor climate in a multipurpose arena located in Malmö, Sweden, with a seating capacity of 13,000 individuals, and in which a combination of displacement and zoning ventilation was applied. The main objective was to explore thermal conditions, indoor air quality, airflow patterns and air distribution. The measured operating conditions were ice hockey game and training situation. The measurements were conducted to observe the indoor climate and computational fluid dynamics (CFD) simulations were performed to get a generic view of the air distribution and the flow field over the whole arena indoor environment. The results show that air movement was highly case-dependent. However, the experiments indicated an upward flow along the lower seating area and a downward flow along the upper seating area. During the game, the average rise of temperature was around 2 °C in arena with low stratification while using displacement ventilation. The temperature range was 12–17 °C at the lower seating area and 15–17 °C at the upper seating area. The corresponding air-speed level was 0.06–0.36 m/s. The relative humidity was about 30%–40% where a part of the humidity was transferring into the ice sheet. The carbon dioxide concentration increased locally to near 900 ppm indicating reasonable operation of ventilation. The CFD simulations predicted well-mixed conditions in arena, thus supporting the measured low-temperature stratification. Overall, the air movement was significantly affected by supply air temperature, variable airflow rates and retractable stand position (on–off) in the arena enclosure. The results support the use of displacement and zoning ventilation in multipurpose arenas.

Indoor hygrothermal condition and user satisfaction in naturally ventilated historic houses in temperate humid continental climate around the Baltic Sea

Indoor climate and user satisfaction were analysed by field measurement and a questionnaire in 67 traditional rural houses in Estonia, Finland and Sweden. Our findings showed that the indoor climate in all the investigated historic rural houses needs improvement. The room temperature was mainly too low during winter. Leaky houses had also a larger vertical temperature difference. The relative humidity in the unheated and periodically heated houses was high during winter and caused risk for mould growth in 17% of all houses and 33% of unheated houses. Significant differences of indoor humidity loads in different houses were revealed depending on the living density and usage profile. During the winter period, the design value of moisture excess was 4–5 g/m3 and the average moisture load was 2–3.5 g/m3. The indoor humidity load in historic houses was similar to that in modern houses. The results of the questionnaire showed that main problems were related to unstable or too low temperatures. At the same time, inhabitants rated the overall indoor climate as healthy and no statistically important relations were found between average indoor temperature and complaints about too cold or too warm indoor temperatures.

Economic viability of energy-efficiency measures in educational buildings in Finland

The economic viability of novel energy-efficient design concepts has been evaluated in Finnish educational buildings. The total energy consumption of representative target buildings with each design concept has been found using the whole-building simulation tool IDA Indoor Climate and Energy 4.0, and the financial viability has been assessed using the discounted payback period method. Different thermal insulation and air tightness properties of the building envelope, and different ventilations heat recovery efficiency assumptions and heat distribution options have been investigated. The results suggest that a prudent attitude should be taken toward the investments in ultra-low-energy designs. Total energy-saving potential of 25–32% can be obtained. The payback periods varied from 15 to more than 40 years. The results can be generalized in cold climates and techno-economic conditions similar to Finland.

Cost-optimal energy performance measures in a new daycare building in cold climate

ABSTRACT New municipal service buildings must be energy effective, and cost-optimality is one of the criteria for selecting the suitable energy performance improvement measures. A daycare building in a cold climate was studied by means of simulation-based, multi-objective optimisation. Using a genetic algorithm, both target energy use and life-cycle cost of the selected measures were minimised. It was found that extensive insulation of the building envelope is not a cost-optimal method to reduce the daycare building energy use. Improving energy efficiency of the ventilation system, utilising solar energy on-site and employing a light control strategy are preferable ways of improving the building energy performance. Ground-source heat pump is a more cost-optimal heating system for the daycare building than district heating. The cost-optimal sizing of the heat pump is small, only 28% of the required maximum heating power. Abbreviations: AHU: air handling unit; CAV: constant air volume; COMBI: comprehensive development of nearly zero-energy municipal service buildings; COP: coefficient of performance; DH: district heating; DHW: domestic hot water; EPBD: energy performance of buildings directive; EU: European Union; FINVAC: Finnish Association of HVAC Societies; GSHP: ground-source heat pump; HRU: heat recovery unit; IDA ICE: IDA Indoor Climate and Energy; LED: light-emitting diode; MOBO: multi-objective building optimisation tool; NSGA-II: Non-dominated Sorting Genetic Algorithm II; nZEB: nearly zero-energy building; PV: photovoltaic; TRY: test reference year; VAV: variable air volume; ZEB: zero-energy building

A cost-optimal solar thermal system for apartment buildings with district heating in a cold climate

ABSTRACT Finding the global optimal combination of the main components for a solar thermal energy system is an important topic in utilising solar radiation in a cost-effective way. However, selecting an optimal solar thermal system in a cold climate condition is a challenging task due to the dependency on the heat demand and the limited availability of solar radiation. This research presents several sets of optimum combinations of a solar thermal collector and a hot water storage tank regarding energy efficiency and the life cycle cost. Since domestic hot water consumption forms the significant part of the heat demand in new energy efficient apartment buildings, the applied consumption information were extracted precisely according to measured data. The solar thermal system with cost-optimal component sizes was able to save district heat energy consumption up 24% to 34% and made 4 €/m^2 to 23 €/m^2 in financial profit.