Toke Rammer Nielsen

Energy performance of glazings and windows

The purpose of the work is to make it possible to compare the energy performance of different glazings or windows in an easy way. The energy performance is expressed by the net energy gain, which is given as the solar gain minus the heat loss. The net energy gain from glazings and windows both depend on the thermal transmittance (the U-value) and the total solar energy transmittance (the g-value). This fact makes it difficult to choose the glazings or windows with respect to energy performance in a given case. To compare different glazings or windows in an easy way, diagrams have been produced which give the net energy gain based on the orientation, the tilt, the U-value and the g-value of the glazings or windows. In addition, a single diagram showing the net energy gain in a one-family house has been produced which takes into account the orientation of the windows in the building. This makes it possible to evaluate the energy performance of different glazings or windows for a one-family house using a single diagram. The diagrams give an easy way of comparing different glazings or windows so the best solution in a given case can be chosen. In addition, the diagram showing the net energy gain in a one-family house is used in the Danish Energy Labelling and Rating system for classification of glazings.

The effect of different weather data sets and their resolution on climate-based daylight modelling

Climate-based daylight modelling is based on the available weather data, which means that the weather data used as input to the daylight simulations are of great importance. In this paper, the effect on the outcome of the daylight simulations of using one weather data file rather than another for the same location was investigated. Furthermore, the effect of using weather data sets with an hourly resolution compared to a one-minute resolution was investigated. The results showed that the lighting dependencies varied by up to 2% depending on the chosen weather data file and indoor illuminance threshold. The energy consumption for artificial lighting was underestimated when simulating with time steps of hourly means compared to one-minute resolution. The findings from this comparison show that the dynamic, short-term effects of the weather have a surprisingly small impact on the simulation outcome.

Illuminance Level in the Urban Fabric and in the Room

The decisions made on the urban planning level could influence the building design at later stages. Many studies have shown that the utilisation of daylight in buildings would result in significant savings in electricity consumption for lighting, while creating a higher quality indoor environment. The surroundings of a building have a great influence on the indoor environment of that building. A major factor is the shading that the surrounding buildings could provide, blocking and diminishing the available amount of daylight in nearby buildings. This paper reports a study that combine the effect of the exterior illuminance levels on façades with the interior illuminance levels on the working plane. The paper also explains an easy to use tool (EvUrban-plan) developed by the authors, which was applied to their findings in the early stages of urban planning to ensure daylight optimisation in the buildings.

Simulation of annual electric lighting demand using various occupancy profiles

This paper describes an investigation of the effect on electric lighting demand of applying occupancy models of various resolution to climate-based daylight modelling. The lighting demand was evaluated for a building zone with the occupant always present, with occupancy corresponding to absence factors, based on an estimated annual mean occupancy, based on estimated 1-hour mean occupancy, and based on 2-min occupancy intervals. The results showed little difference in the annual electric lighting demand when the same occupancy profile was used every day, as opposed to when profiles were used where occupancy varied every day. Furthermore, the results showed that annual electric lighting demand was evaluated slightly conservatively when a mean absence factor was applied as opposed to using dynamic occupancy profiles.

System Design for Demand Controlled Ventilation in Multi-Family Dwellings

Abstract This paper presents an investigation into solutions for the system design of a centralized DCV system in multi-family dwellings. The design focused on simple and inexpensive solutions. A cost benefit estimate showed that the initial cost of implementing DCV in a system with an efficient heat exchanger should not exceed 3400 DKK per dwelling in regions with weather conditions similar to the Danish climate. A design expected to fulfil this requirement was investigated in detail with regard to its electricity consumption by evaluation of different control strategies. Systems with variable airflows are typically controlled by maintaining the static pressure at a fixed level at a selected point in the main duct. However, sustaining the static pressure at a fixed level at part load leads to throttling of all control components and thereby unnecessary energy consumption. Resetting the static pressure at part load reduces throttling and energy can be saved. A static pressure reset strategy was applied to a dwelling-specific DCV system where the airflow varied between three fixed rates. The system performance was evaluated for two diffusers. The annual electricity consumption was reduced by 20% to 30% when resetting the static pressure at part load condition compared to a control strategy with fixed static pressure.