A new HVAC ductwork steady-state flow analysis method: The Minimum Energy Dissipation Principle applied to flow networks including the effects of branched junctions

The fact that the popular head loss coefficient concept, may become negative in branched junctions, is a symptom that something is not correctly managed. The paper makes a review of recent works which have sought new models based on physical concepts, as a way to avoid speaking about “negative losses”. Herwing and Schmandt [1], showed that the origin of the negative sign was a diffusive shear work exchange between the two streams of a branched junction. Traditionally, the head losses at the branched junctions are neglected, but definitely it cannot be done in HVAC air-duct networks. Firstly, the paper illustrates how, by ignoring this “negative loss” contradiction, traditional duct network analysis may encounter unexpected numerical difficulties. Secondly, it shows that the Minimum Energy Dissipation Principle (MinEDP) can be successfully applied to analyze the steady-state of any flow network (not necessarily HVAC ductworks), with or without shear work at junctions. Moreover, the new method does not need to know the latter, beforehand, although the nature of the solution is very different in either case. Finally, the paper includes a practical example of an HVAC ductwork to illustrate the outcomes. The new method works smoothly and quickly and does not need any ad hoc modification to cope with an eventual “negative” head loss

Discrete event heat transfer simulation of a room using a Quantized State System of order two, QSS2 integrator

[EN] In a previous paper [1] it was shown a proposal for a discrete event simulation (DEVS) model of a thermal zone. A quantized state integrator of order one (QSS) was used to integrate the evolution of the room air temperature. In order to increase the computational speed, this paper presents how the multi-layered wall, 1D conduction heat flow dynamics could be modified to allow its use with a second order QSS2 quantized integrator. The almost forgotten successive transition state method (see U. Yoshimi et al. [2]) is modified with changes in the hold function. Finally to validate the results, a test room has been employed to compare the results with EnergyPlus v7.1. Three cases have been studied: fixed T zone , floating T zone and floating T zone plus a random convective heat gain.Soto Francés, VM.; Sarabia Escrivà, EJ.; Pinazo Ojer, JM. (2015). Discrete event heat transfer simulation of a room using a Quantized State System of order two, QSS2 integrator. International Journal of Thermal Sciences. 97:82-93. doi:10.1016/j.ijthermalsci.2015.06.006S82939