• Energy Research

Abstract Geothermal systems are often employed for both the heating and cooling of sustainable constructions. Energy piles (U-shaped heat exchangers inserted into the foundation piles) are widely included in these installations, whose performance is usually estimated by means of complex, time-consuming simulations already at an early design stage. Here we propose a simple methodology, where a hand calculation tool provides the condenser yield per pile meter, ground area yield and demand covered by the heat pump by specifying only building heat load and geometric characteristics of the energy piles field. Our tool is tested by assuming 20 years of operation in a hall-type commercial building in a cold climate. A validated IDA-ICE parametric study couples the heat pump evaporator operation with heat transfer processes between energy piles and soil. Various system configurations are considered and thermal storage in the soil is included. We find that the expected yield is not directly proportional to pile separation, while a smaller extraction power is favoured. Thermal storage in the soil is also confirmed to be critical. Besides our specific quantitative results, our practical guideline is qualitatively general and can be extended to any given building type and climate.

| openaire: EC/H2020/856602/EU//FINEST TWINS Publisher Copyright: © 2023 International Building Performance Simulation Association (IBPSA). This paper investigates how a simulated room’s energy and temperature performance are affected if its underfloor heating control is modelled with increasing detail. Experiments were performed to develop and calibrate an empirical model of wax motor and to calibrate the valve curve. These models were used to implement and test the On/Off and proportional-integral (PI) control processes at various levels of modelling detail. Controllers were implemented by gradually adding optimized control parameters, signal delay, calibrated valve curve, signal modulation, and actuator modelling. The On/Off control dead band and PI parameters exhibited the largest impact, reducing energy use (1%–5%) and temperature fluctuations (ca 1 K). Modulating the PI output signal increased temperature fluctuations to the same amplitude as On/Off with 0.5 K dead band, increasing space heating demand by 1.3%. The wax actuator counted for less than 1%; however, it increased time delays to maximally 7 min and remarkably changed the mass flows. Peer reviewed

Energy renovations of the building stock are a paramount objective of the European Union (EU) to combat climate change. A tool for renovation progress monitoring is energy performance certificate (EPC) labelling. The present study tested the effect of different EPC label classifications on a national database, which comprises ~25,000 EPC values from apartment buildings, detached houses, office buildings, and educational, commercial, and service buildings. Analysing the EPC classes labelling resulting from four different EU methods, we estimated the annual renovation rates, costs, energy savings, and CO2 emissions reduction that would affect the national building stock if each of them was adopted, to fulfil the European Climate Target Plan by the year 2033. The ISO 52003-1:2017 two-point and one-point methods determined a very uneven distribution of renovation rates, from 0.45% to ~9%. Conversely, the Directive 15% recently proposed in COM/2021/802 with uniform rates determined smaller differences and standard deviation, not pushing renovations above 3.70%, namely a rate that once fine-tuned can stimulate realistic, yet effective renovation campaigns. The major differences in renovation rates provided by the studied methods show the need for a harmonized strategy such as the Directive proposal to enable achievement of European targets.

Heat emitters constitute the primary devices used in space heating and cover a fundamental role in the energy efficient use of buildings. In the search for an optimized design, heating devices should be compared with a benchmark emitter with maximum heat emission efficiency. However, such an ideal heater still needs to be defined. In this paper we perform an analysis of heat transfer in a European reference room, considering room side effects of thermal radiation and computing the induced operative temperature both analytically and numerically. By means of functional optimization, we analyse trends such as the variation of operative temperature with radiator panel dimensions, finding optimal configurations. In order to make our definitions as general as possible, we address panel radiators, convectors, underfloor (UFH) and ceiling heater. We obtain analytical formulas for the operative temperature induced by panel radiators and identify the 10-type as our ideal radiator, while the UFH provides the best performance overall. Regarding specifically UFH and ceiling heaters, we find optimal sizes that identify the according ideal emitters. The analytical method and quantitative results reported in this paper can be generalized and adopted in most studies concerning the efficiency of different heat emitter types in building enclosures.

The buildings’ energy performance requirements in Estonia are based on cost-optimality analysis according to the EPBD and pre-defined building performance simulation (BPS) input data from EN 16798-1:2019. Previous studies have shown that the real electricity use of office building tenants differs from the currently used input data in BPS in Estonia – less in total energy use, but more in the shape of the profiles. The aim of this work is to investigate what is the impact of these differences on the cost-optimal solutions, which are identified based on BPS and the self-consumption of the photovoltaic panel (PV) systems. This study describes the energy performance and construction cost analysis of a new office building in Tallinn, Estonia. BPS based on the EN 16798-1 and a model derived from measurements in a real building were conducted and cost-optimal building solutions identified. The variables were building envelope insulation thickness, air handling unit size and effectiveness, electrical lighting control principles and PV system nominal power. The calculated energy use of the building with the two different sets of input data differed significantly. However, the set of cost-optimal solutions identified with EN 16798-1:2019 input data had minor differences from the set of solutions identified with the more realistic model. The decrease of net present value over 20-year period for cost-optimal solution was 11-14 €/m2 compared to the designed building.The realistic office tenants’ electricity model increased the calculated self-consumption of the PV system from 95% to 100%.

Large office buildings are responsible for a substantial portion of energy consumption in urban districts. However, thorough assessments regarding the Nordic countries are still lacking. In this paper we analyse the largest dataset to date for a Nordic office building, by considering a case study located in Stockholm, Sweden, that is occupied by nearly a thousand employees. Distinguishing the lighting and occupants’ appliances energy use from heating and cooling, we can estimate the impact of occupancy without any schedule data. A standard frequentist analysis is compared with Bayesian inference, and the according regression formulas are listed in tables that are easy to implement into building performance simulations (BPS). Monthly as well as seasonal correlations are addressed, showing the critical importance of occupancy. A simple method, grounded on the power drain measurements aimed at generating boundary conditions for the BPS, is also introduced; it shows how, for this type of data and number of occupants, no more complexities are needed in order to obtain reliable predictions. For an average year, we overestimate the measured cumulative consumption by only 4.7%. The model can be easily generalised to a variety of datasets.