Theoretical and Experimental Investigation of a Heat Exchanger Suitable for a Hybrid Ventilation System

Abstract

A key component in low energy houses is the heat recovery from the ventilation air. Over recent years, the most frequently used ventilation type is the mechanical ventilation with heat recovery. This kind of ventilation results in high heat recovery but does unfortunately consume a considerable amount of electrical energy. Natural or hybrid ventilation has the potential to consume less electricity but normally lacks heat recovery, leading to high-energy consumption for heating, and potentially low comfort. This article describes an investigation of a natural/hybrid ventilation system equipped with heat recovery. One of the key challenges in designing the heat exchanger is to keep the pressure drop low. At the same time the heat recovery rate has to be high. The results from the measurements show that it is possible to design a water-to-air heat exchanger with a temperature efficiency of approximately 80% with a pressure drop of about 1 Pa at air flows corresponding to 0.35 L/(s·m²) building area. This type of ventilation system has the potential to offer a high thermal comfort, high heat recovery rate at the same time as the electrical consumption from fans is kept low. Old buildings with a natural ventilation system without heat recovery could also be retrofitted with this type of ventilation system.

Interaction between Thermal Comfort, Indoor Air Quality and Ventilation Energy Consumption of Educational Buildings: A Comprehensive Review

“…Hwang et al [97] demonstrated that thermal perceptions of students were significantly related to the air temperature, wind speed and solar isolation, while the influence of acoustic, lighting and IAQ aspects can be ignored [97]. Davidsson et al [104] pointed out that thermal comfort is related to the heat recovery rate. Mishra et al [99] assessed the thermal comfort perception of students through the class hours, and they found that the thermal perception varied primarily with the outdoor temperature, operative temperature, and their previous thermal conditions.…”

Hybrid Ventilation with Innovative Heat Recovery—A System Analysis

“…In Figure 3 it can be seen that, for the hybrid ventilation system to perform as well as the mechanical ventilation system, the heat exchanger has to have an efficiency of about 86%. A heat recovery efficiency of 86% on a component level equals a system heat recovery rate of 75% [4], i.e., when both the roof and the heat exchanger at the bottom of the building are taken into account. This means that the need for auxiliary energy is the same for both systems.…”

“…One alternative is to construct the heat exchanger in such way that it allows for cleaning. This is possible since the structures in the heat exchanger are in the order of centimeters [4] and not millimeters as in the case of the heat exchangers of mechanical systems.…”

“…At the same time, the units have a risk of creating a disturbing noise from the ventilation system. Recently, there have been reports about heat exchangers designed to work in natural or hybrid ventilation systems [3,4]. The heat exchangers have a very low pressure drop, down to or even less than 1 Pa, and at the same time high heat transfer rates in the units.…”

Heat Loss for a Run-Around Hybrid Ventilation System with Heat Recovery

“…One possibility could be to install hybrid ventilation systems with heat recovery. Recent development concerning heat exchangers with very low pressure drop has made these types of systems possible, Hviid andSvendsen (2011), andDavidsson et al (2013a). These types of heat exchangers can be used in run-around heat recovery systems, Davidsson et al (2013b).…”