Comparison of Single- and Multipipe Earth-to-Air Heat Exchangers in Terms of Energy Gains and Electricity Consumption: A Case Study for the Temperate Climate of Central Europe

Earth-to-air heat exchangers (EAHEs) can be used in the ventilation systems of various types of buildings. Multipipe structures can be found in large-volume buildings, yet scientific analysis of such systems is rare. Annual energy gains and electricity consumption for equivalent single-pipe and multipipe systems are typically not available. This paper bridges this gap, presenting the results of experimental studies on pressure losses in three-, five- and seven-pipe EAHEs and analysis for the annual energy gains and electric energy consumption as compared to a single-pipe exchanger. The results showed that the multipipe EAHE can be successfully replaced by a single-pipe structure with the same thermal performance and similar pressure losses if a tube with the appropriate diameter is used. However, multipipe heat exchangers can also use pipes of larger diameter (manifolds and/or branches), which improves their energy efficiency and may then make them more advantageous than single-pipe structures. From this reason, ultimately, the final selection of exchanger geometry should take into account economic and environmental issues and also user preferences and their importance in the hierarchy.

Stability and Modal Conversion Phenomenon of Pipe-in-Pipe Structures with Arbitrary Boundary Conditions by Means of Green’s Functions

In this paper, a closed-form frequency equation of the pipe-in-pipe (PIP) structure with arbitrary boundaries is obtained. The frequency equation is derived from Green’s function of the transverse forced vibration of the PIP structure and takes into account the effects of internal two-phase flow and axial pressure. The reliability of the method in this paper is proved by comparison with the published literature. In the numerical discussion part, the PIP structures with clamped-clamped, clamped-free, and elastic boundary conditions are used as examples to discuss. The effects of equivalent stiffness coefficient, internal flow velocity, and gas volume fraction on the stability of PIP structure are studied. The results show that the stability of the PIP structure is better than that of the single-pipe structure, and the greater the equivalent stiffness coefficient of the elastic layer, the higher the critical flow velocity of the structure. In addition, a modal conversion phenomenon existing in the PIP structure is discovered. There are different forms of modal conversion for different boundary conditions, and the modal conversion makes the order of instability of the PIP structure different from that of a single-pipe. The conclusion of this paper has positive significance for the dynamic research of PIP structure.

Estimation of the influence of hydraulic balancing of the heating system and shading of external enclosures on the energy consumption of the university building

The main design features of single-pipe systems with vertical wiring, the reasons for their low efficiency, which include: physical and moral obsolete equipment and pipeline valves, lack of automatic control and regulation of coolant supply, low efficiency of heating devices, are characterized. Using the methodology according to DSTU B V.2.6-189-2013 and DSTU B A.2.2-12: 2015, the effectiveness of the introduction of automatic balancing of the heating system was first investigated, and then the effect of shading of external enclosing structures on the energy consumption of the university building, taking into account the existing state of external enclosing structures ... It has been established that balancing the heating system makes it possible to reduce the specific energy consumption for heating by 7.6%, and to reduce the energy consumption of the heating system by 164.8 MWh. The influence of the shading of external enclosing structures on the energy consumption of the building of the university is estimated, taking into account the existing state of the external enclosing structures in the absence of balancing the heating system of the building. It is shown that it leads to an insignificant excess of energy consumption for heating by 0.3 % or 6.6 MWh. It has been proven that the energy consumption of a building, taking into account the shading coefficient after balancing the heating system, can reduce the specific energy consumption for heating by 7.9 %, and reduce the energy consumption of the heating system by 165.4 MWh. Assessing the effect of shading of external enclosing structures "before" and "after" balancing the heating system of the university building, it can be argued that the energy consumption of the heating system has been reduced by 158.8 MWh or by 7.7 %. Key words: flow, balancing, solar insolation, heating system, shading

SARS-CoV-2 adsorption on suspended solids along a sewerage network: mathematical model formulation, sensitivity analysis, and parametric study

Accounting for SARS-CoV-2 adsorption on solids suspended in wastewater is a necessary step towards the reliable estimation of virus shedding rate in a sewerage system, based on measurements performed at a terminal collection station, i.e., at the entrance of a wastewater treatment plant. This concept is extended herein to include several measurement stations across a city to enable the estimation of spatial distribution of virus shedding rate. This study presents a pioneer general model describing the most relevant physicochemical phenomena with a special effort to reduce the complicated algebra. This is performed both in the topology regime, introducing a discrete-continuous approach, and in the domain of independent variables, introducing a monodisperse moment method to reduce the dimensionality of the resulting population balance equations. The resulting simplified model consists of a large system of ordinary differential equations. A sensitivity analysis is performed with respect to some key parameters for a single pipe topology. Specific numerical techniques are employed for the integration of the model. Finally, a parametric case study for an indicative—yet realistic—sewerage piping system is performed to show how the model is applied to SARS-CoV-2 adsorption on wastewater solids in the presence of other competing species. This is the first model of this kind appearing in scientific literature and a first step towards setting up an inverse problem to assess the spatial distribution of virus shedding rate based on its concentration in wastewater.

Heat transfer assessment of multi-tier chilling pipes for root zone cooling system under crop protection structure in the tropics

Root zone cooling technique has become an alternative cultivation method for temperate crops production in the tropics instead of cooling the aerial environment of the greenhouse. In this experiment, the root zone cooling system was incorporated with a multi-tier crop cultivation structure. This structure consisted of five tiers arranged in an A-shape design and was placed under an open rain shelter, thus, left it to undergo fluctuating environment temperature. There were five pillow polybags inserted with cocopeat and were placed on the structure. Each pillow polybag consisted of a single pipe that was buried inside the growth media located near the root zone area. This pipe that was connected to the chilled system acted as a cooling agent in controlling the growth media temperature. The objective of the study was to evaluate the Root Zone Cooling (RZC) system performance in distributing and controlling water-dissolved nutrient temperatures to meet crop-root requirement needs. From the experiment conducted, it was found that there was no significant difference between root zone temperature at different levels and lengths on multi-tier structure. The chilling pipes was able to distribute the temperatures to meet crop-root requirement needs along the multi-tier structure.