Göran Hultmark

Analysis of control strategies for a novel HVAC system equipped with a room-temperature water loop

This article presents a simulation-based study that investigated four control strategies to regulate a novel two-pipe system for office buildings. The main characteristic of the system is its ability to provide simultaneous heating and cooling by operating a single water circuit with supply temperature of about 22◦C. The study was conducted by considering a typical office building model in two different climates, Chicago (US) and Copenhagen (Denmark). Simulations were performed in Dymola, a commercial simulation environment for Modelica models. The four control strategies ranged from linear SISO (single input, single output) to PI (proportionalintegral) feedback controllers with detailed information about the indoor climate in the building. Results showed that all the four strategies were able to maintain comfortable levels of indoor air temperatures in the zones. With regard to the annual energy use, savings of about 7-10% were achieved when comparing PI feedback controllers with SISO strategies.

Procedure for Balancing an Air Distribution System with Decentralised Fans

AbstractThis paper presents results from an on-going project concerning new design procedures for mechanical ventilation systems with low energy use. Conventional constant air volume (CAV) systems are usually balanced using flat plate dampers. The purpose of using balancing dampers is to intentionally introduce pressure drops in the duct system thus nominal airflows are achieved throughout the ductwork within specified tolerances. However, introduction of pressure drops will increase energy requirement for the ventilation system and in addition, balancing a duct system is a time consuming task and often flawed. This paper presents a new procedure for balancing of C AV systems in combination with decentralised fans. The new system was based on replacing the balancing dampers with decentralised fans. By replacing the balancing dampers with decentralised fans, airflows can be balanced by adjusting the speed of the fans. In conventional air distribution systems the fan provides the necessary pressure to overc...