Bjørn R Sørensen

An energy efficient control strategy for fan static pressure difference

Ventilation fans are energy-demanding equipment that stand for a significant share of a buildings total energy consumption. Improving energy efficiency of fans is thus important. Fans used for demand controlled ventilation deliver a specific flow rate derived from the actual load in the building. This paper is about how to deliver the required flow rate to all rooms, without wasting energy on throttling. The simulation study shows that by introducing a relatively simple control procedure, the fan can be controlled more efficient and energy consumption can be reduced by as much as 40% (compared to constant set-point pressure difference control).

Analytical Model of Capillary Suction Velocity of a Pipe with Multiple Sizes

Absorption of water in concrete is often described by simple linear water uptake vs. square-root-of-time law. This model based on the classical capillary model derived from the Hagen-Poiseuille’ flow which travel on a single pipe dimension. However, in cement-like material concrete, the pore structure is complex, including for example, variable pore radius and complicated topological changes. In this work, an analytical velocity model of Hagen Poiseuille’s flow on a pipe with multiply sizes is constructed. This model takes the pipe geometry as described by two sets of parameters α_i and β_i;i=1,2…,N into account. In addition, a numerical study of other flow models using Navier Stokes and Stokes models has been conducted. The analytical model is in good agreement with the numerical models at a series of different pipe geometry sizes.

Establishment and Instrumentation of a Full Scale Laboratory for Thermal and Hygroscopic Investigations of Soil Behavior in Cold Climates

This study presents the establishment and instrumentation of a laboratory for investigating how different soils behave under controlled conditions in cold climates. Ground conditions are extremely important in regards to the building sector. Establishing new infrastructure and buildings require high competence about the ground/soils in order to build robust and long lasting foundations and constructions. In cold climates, soils are frequently exposed to freezing and thawing cycles, and building projects often require additional resources compared to similar projects further south. During 2009-2010, a new laboratory was established in Narvik, Norway. The laboratory consists of 4 different 6x6m bins containing different homogenous soils down to a depth of 3m. A special designed measurement frame has been placed inside each bin, which facilitates instrumentation for thermal and hygroscopic measurements. The laboratory has many applications which may lead to advances within knowledge about thermal response of soils, artificial thawing for more efficient building in cold climates, faster dehydration and curing of concrete during winter, improved road foundations and preventing frost heaves and so on. This study describes the laboratory setup and presents test measurements on thermal responses of sand, silty sand and gravel during artificial thawing using a hydronic thawing system.

Thaw Penetration in Frozen Ground Subjected to Hydronic Heating

Acknowledgments This study is funded by Nordland County council, the ColdTech project (RT4-01), and Heatwork AS. The authors are grateful for the support in establishing the Frost in Ground laboratory (FiG-lab) and the access to the facilities during this work. The authors also thank Heatwork AS for providing the defrosting system used during the experiments.

Heat Transfer Coefficients and Dynamical Thermal Models for Variable Flow Rates in Pipes and Ducts

This study presents thermal models of pipes or ventilation ducts with variable flow rates. The models are based on dynamic thermodynamic heat balances, and much attention has been put into developing accurate heat transfer coefficients. MATLAB/Simulink environment has been used for modeling, but the model is however universal and can be implemented into any software. The model has been validated against measurement data, and found to be quite accurate for use in typical HVAC applications. Accuracy is particularly good if taking thermal damping into account. Thermal damping of pipe or duct mass has shown to be significant for dynamic performance. The model is suited for control simulations or accurate heat loss simulations, where dynamic conditions are important.

Integration of Multiple In-House Heat Stations into One Energy Flexible Heat System

This study is focused towards assessing the potential for energy savings and cost reduction by integrating multiple in-house heat stations in several buildings into one larger energy flexible heat system. All existing boilers in stand-alone systems are kept as production units of a new merged system, and will be in addressed and operated when the condition demands it. In this study, energy and cost calculations are done on an hourly basis. Which combinations of boilers to be used in each time step are determined from the lowest running cost for each time step. The results of the case study show a clear savings potential for both energy and costs.

The Influence of Oversized Boilers on Power Efficiency, Energy Consumption and Cost in Energy Flexible Heat Stations. Part 1

Oversized boilers in in-house heat stations are relatively common. This study demonstrates the effect of installed overcapacity in heat stations with regard to the buildings heat load. Potential energy savings are calculated on basis of a heat station containing both fuel oil boiler and electric boiler. Correct installed capacity is defined as the capacity of a boiler designed to meet the design outdoor temperature, DOT. The baseline for normal consumption has been defined by utilization of correct designed boilers operated under various climatic conditions for a normal year. This baseline has then been compared to consumption calculation done with oversized boiler capacity. The energy consumption calculation is done on an hourly basis for one year. The results show a clear connection between the boiler size, boiler efficiency and potential savings in energy and cost.

Energy Efficient Control of Fans in Ventilation Systems

Ventilation fans are energy-demanding equipment that stands for a significant share of a building’s total energy consumption. Improving energy efficiency of ventilation fans is thus important. Fans used for demand controlled ventilation (DCV) are intended to deliver a specific flow rate derived from the actual load in the building. This chapter is about how to deliver the required air flow rate to all rooms, without wasting energy on throttling. There are several ways to control the flow rate in a ventilation system. The most common ways are (1) pure throttling, (2) constant differential pressure and (3) constant duct static pressure. In some situations, (4) direct fan control are used as a control strategy (DDCV). The latter is known to be efficient, as it will provide only the required air flow at all times, without the need for any throttling. It needs however more extensive instrumentation, and flow rates to and from all zones in a building have to be continually recorded and fed back to the central flow controller. A simulation study shows that by introducing a relatively simple control procedure, the fan can be controlled more efficient and energy consumption can be reduced to a significant degree, also for alternative (2) and (3), without the need for added control equipment.