Issue 6/2017

The paper deals with the acoustic assessment and design of acoustic protection for an actual heat pump system for a residential building with a shop installed in the courtyard of an older residential building. The heat pump system is used for the cooling and heating of the residential and non-residential premises, hence the night operation of the heat pumps, which is subject to stricter hygiene limits on noise. The installation of the units and the construction were already under implementation, therefore, there was little room for acoustic design adjustments.

The energy system consisting of a combined ground-air source heat pump, PV system and seasonal ground storage unit for an energy passive family house has been developed and analysed by computer simulation. The heat pump, during summer operation, transforms the ambient heat to charge the seasonal ground storage with the use of PV electricity only. Winter operation relies on the heat stored under the house and results in low grid electricity consumption. The simulation analysis has shown the significant decrease in the use of the grid electricity needed for the house (the system’s SPF increased from 3.1 for the reference borehole system to about 6.0) and an increase in usability of the local PV electricity production for energy supply (space heating, hot water) in the house. In total, more than 80 % of the energy supply for the house is renewable energy and the specific non-renewable primary energy needs of the house is under 17 kWh/m·a (for space heating, hot water and auxiliary energy).

Recent trends in building construction in central Europe show a growing number of well insulated residential buildings. The heat demand for domestic hot water preparation is, in those applications, similar or higher than for space heating. Regular vapour-compression heat pumps reach a relatively low SPF 2.5 in such applications. The way to increase SPF is to use a heat pump with multiple heat exchangers on the highpressure side (desuperheater, condenser, and subcooler) and a special hot water storage tank with three internal heat exchangers for good temperature stratification. A prototype of a heat pump with a desuperheater and subcooler was developed and a mathematical model of a refrigerant cycle was tested on it. The model of the heat pump describes the heating capacity and power input with an average relative deviation lower than 5 %. The validated model was used in simulations of a system for hot water preparation in a block of flats. The water draw in the simulation was set under the European standard and measured data from real applications. The results of simulations show SPF improvement by 26 % for a heat pump with a desuperheater and subcooler in comparison with a standard heat pump.

A previously developed approach to simplify the numerical modelling of heat sources based on the replacement of a heat source by a simple boundary condition (see VVI 5/2012) is applied in the real scenario of a recently refurbished former church built in the 14th century. The building is now used as a concert and conference hall with up to 350 visitors staying for different time periods during each day. The investor of the restoration was concerned about temperature fluctuations caused by the variable occupancy and the possible negative impact on the historical stucco decorations and on the original wooden trusses of the former church. Moreover, only natural ventilation through window openings on the street level and the windows in the roof is possible in order to preserve the original look of the building. The study elaborated upon in the paper is based on the results of the CFD simulations with simplified models of visitors acting as heat sources under two different occupancy scenarios.

The aim of the contribution is to determine the energy demand for ventilating classrooms with the inclusion of heat gains and to analyse the energy benefits of high heat recovery efficiency. On a simple model of the classroom, a calculation was performed in an ESP-r energy simulation programme and the operating costs of the mechanical ventilation were determined. Part of the contribution is also an analysis of the selected local ventilation units, which leads to the determination of specific financial costs for the operation of the mechanical ventilation. It was found that the total cost of continuous mechanical ventilation with a defined air flow rate is not a crucial element of a school budget.

The paper deals with the specifications of a settable range of air volumes for a personalized ventilation system to provide an appropriate fresh air supply to the user. It mainly deals with the interaction of fresh air flow and human convective boundary layers and the difference in various volumes and velocities. Measurement of the flow interaction was taken by a Particle Image Velocimetry (PIV), using a thermal manikin to simulate the environment around the human body.

This calculation study investigates the impact of the airtightness of a building envelope on the heat demand of a single-family house and a multi-family residential building in the Central European climate (Prague). Both model buildings are passive houses, equipped with a balanced mechanical ventilation system with heat recovery. For the purpose of this study, transient thermal and air infiltration models were developed using Matlab – Simulink. The single-family house was modelled as a single zone building. In the multi-family building, each flat and the staircase were considered as separate pressure zones. Iterative approaches were adopted for the reliable coupling of the thermal and air infiltration models (different in the single and multizone models). Their heat demand was calculated as a function of the envelope airtightness (n50 varying from 0 to 1 h-1). Several combinations of leakage distribution over the building envelope, wind shielding and alternatives of the internal leakage paths between the zones were considered. The heat demand increases noticeably with the building envelope air permeability. The increase is more pronounced in the case of the residential building (e.g., 3 kWh/(m2·a) per unit of n50 against 2 kWh/(m2·a) for the single-family house under the same conditions). The wind shielding and the leakage distribution significantly influence the results. The internal air leakage does not significantly affect the heat demand of the residential building, which mostly depends on the air leakage of the envelope and its distribution. However, significant air flow rates were detected between the zones (up to 24 m3/h between the flats). The internal leakage may, therefore, cause an issue for indoor air quality, ventilation system function and fire safety.