• Making the case for district cooling
    PDF 313 KB
    Today, around 10% of the world’s electricity production is used for air conditioning. According to international studies, the demand for cooling of commercial and residential buildings will grow exponentially in the years to come, especially in high-income countries and emerging economies in India, China and South America.
  • Valve characteristics for motorized valves in district heating substations
    Valve characteristics for motorized valves in district heating substations
    PDF 3.512 KB
    The present paper describes the results from an investigation carried out in connection with the development of a new valve characteristic for motorized control valves for hot water service in district heating (DH) substations. From a theoretical point of view, the paper discusses basic control theories and physical relationships of crucial importance to this application, including the decisively important relationships between heat exchanger, controller, motor (actuator) and control valve. In addition to the theoretical analysis, the investigation is supported by dynamic simulations and results from laboratory experiments. The result of the investigation was the development of a new valve characteristic as described in this paper.
  • Optimum control of heat exchangers
    PDF 4.811 KB
    The present paper concerns the control of high-performance heat exchangers for hot water service. Some of the basic control theories and their decisively important relationships are analyzed from a theoretical point of view. A newly developed control is described, putting the various elements in the design into the perspective of control theory.
  • Distribution systems in apartment buildings
    Distribution systems in apartment buildings
    PDF 3.278 KB
    In an apartment building, the two main principal heat and domestic hot water (DHW) distribution methods are the riser pipe system and the decentralized system with flat stations. In the first case, the DHW system heat losses may be bigger than the net heat for preparing the DHW.
  • Dynamic simulation of DH house stations
    Dynamic simulation of DH house stations
    PDF 3.185 KB
    Danfoss proceeds on developing simulation models of HVAC components including control equipment that the company produces for central and district heating systems. In this paper some examples are given. The example of a simulated domestic hot water service station is presented.
  • How to avoid pressure oscillations in district heating systems
    How to avoid pressure oscillations in district heating systems
    PDF 5.074 KB
    This paper explains the nature of differential pressure controller in relation to oscillation. Some operative hints for eliminating or reducing pressure oscillations are presented. Thanks to the application knowledge in the field of differential pressure control, it is now possible to solve pressure oscillatory problems in already existing applications, and to offer specific advice regarding the right design of new applications in order to eliminate the risk of pressure oscillations. Read full paper to find out more.
  • Auto tuning and motor protection as part of the pre-setting procedure in a heating system
    PDF 819 KB
    Autotuning: Adaptive setting of a domestic hot water service controller. Motor protection: Automatic setting of a controller during low performance. A precondition for a well functioning heating system is that the correct settings are made before it is put to use. Adjustments are necessary to preset the regulating parameters. This article deals with the way in which the automatic setting of system control parameters is performed and the advantages this gives.
  • Pilot controlled valve without auxiliary energy for heating and cooling systems
    PDF 406 KB
    The parallel installation of two valves with different dimensions allows a wide positioning range also for controllers without auxiliary energy. So, high control stability for the low and partial load range can be assured. These ‘pilot controlled control units’ consist of a main valve, a
  • Control concepts for DH compact stations
    PDF 706 KB
    This article describes the basic functionality of four control concepts, a thermostatic controller, a proportional controller and a parallel and serial coupling of those. The focus is on plate heat exchanger control, and the investigation is based on dynamic simulations, i.e. on models verified up against practical measurements.
  • Hydraulic balance in a district heating system
    PDF 756 KB
    Establishing a hydraulic balance in a system often is a matter of controlling the differential pressure to a level necessary for operating the substation and thereby also controlling the flow rate in individual branches. Controlling differential pressure and flow rate in the system can have advantages for customers and utilities.
  • Reducing oscillations in a HVAC system
    PDF 338 KB
    In a HVAC system as well as in a process plant, a district heating and district cooling utility, periodical oscillation of the control loop might occur. It has several reasons. Non linearity of the process, excessive amplification of the controller and an oversized system are just few of the reasons.