Low Temperature Heating and High Temperature Cooling in Buildings

Abstract

A heating and cooling system could be divided into three parts: terminal units (emission system), distribution system, and heating and cooling plant (generation system). The choice of terminal unit directly affects the energy performance, and the indoor environment in that space. Therefore, a holistic system evaluation is necessary to ensure an optimal indoor environment for the occupants and to achieve energy efficiency simultaneously. Low temperature heating and high temperature cooling systems are one of the possible approaches to heat or cool indoor spaces in buildings. In this thesis, a single-family house designed for plus-energy targets and equipped with a radiant water-based floor heating and cooling system was studied by means of full-scale measurements, dynamic building simulations and thermodynamic evaluation tools. Thermal indoor environment and energy performance of the house were monitored for one year while different control strategies were tested. Theoretical analyses consisted of comparing the performance of different heating and cooling systems using energy, exergy, and entransy methods under steady-state conditions. Dynamic simulations were used to study the energy performance of heating and cooling systems for achieving the same thermal indoor environment. The results show that it is crucial to minimize the heating and cooling demands in the design phase since these demands determine the terminal units and heat sources and sinks that could be used. Low temperature heating and high temperature cooling systems (a radiant water-based floor heating and cooling system in this study) proved to be superior to compared systems, evaluated with different system analysis tools; energy, exergy, and entransy. Radiant systems should be coupled to appropriate heating and cooling sources, and energy requirements of auxiliary components (pumps, fans, etc.) should be minimized. Radiant systems could be coupled to renewable heat sources and sinks (e.g. ground), which would result in considerable energy savings. Water-based heating and cooling systems require considerably less auxiliary energy compared to air-based systems. Exergy analysis can be used to optimize a system holistically where different quality energy forms, such as electricity and heat, are used. Control of the radiant system and its interaction with the ventilation system are critical for an optimized operation. Measurements, simulations, and calculations proved that a system in which the radiant system heats or cools the space and the ventilation system only provides the required amount of fresh air for indoor air quality concerns is the optimal solution. Application of radiant floor heating is particularly beneficial in high-ceilinged spaces, as it can provide a uniform temperature distribution and decrease heat losses due to thermal stratification. To obtain the most rational use of available resources, energy analysis alone is not sufficient. It is not enough to consider only the quantity of energy; the temperatures and temperature differences within a system should also be considered. Although a single-family house was used for evaluations in this thesis, the results and developed calculation methodologies can be applied to a wider range of buildings using similar heating and cooling systems.