Powerhouse Telemark: A plus energy building with a low exergy heating and cooling system

Abstract

Powerhouse Telemark (PHT) is an eleven stories high office building in Telemark in Norway, built to plus energy standard. A plus energy building that is built according to the Powerhouse definition prior to 2019 must produce more renewable, locally produced energy during the lifetime of the building, and must produce enough renewable energy to cover the total embodied energy used for the production and transportation of the building materials used in the building. The local renewable energy production must also cover the yearly net energy needs for operations, renovations and demolition of the building. The local production of renewable energy on the building is not required to cover the energy needed for plug loads in the building.The building will have a unique diamond shape, and the roof of the building is oriented towards the south, and slopes at an angle of 24 degrees from the horizontal. The building will be a net supplier of electricity when seen over a whole year.In addition to other “normal” measures to achieve a plus energy building, like a high performance building envelope, and an extremely efficient ventilation system, energy efficient lighting and equipment and a solar PV system, a new low exergy heating and cooling system has been implemented in the building. This low exergy system (called Lowex) is based on low temperature heating and high temperature cooling, which together with an optimized energy well design will give extremely low demand for delivered energy (electricity). To design this Lowex system, a lot of different calculations and simulations had to be done, both with commercial software packages, but also with new develop dynamic simulation models. These design procedures and models are described in this paper. This paper also describes how these results will be used for the operation of the building.The building is currently under construction and will be commissioned in late 2019/early 2020. The main experience from the design phase and early construction phase is that the Lowex system sets strict demands on both façade design and the interior design. Transparent vs. opaque area ratios, solar shading and glazing solutions set boundaries for the architectural concept, and must be taken into account early in the design process. Flooring materials, ratio of landscape vs. office cells, and thermal zoning of the building affects the interior design. The acoustic concept and the carbon footprint of the building as well as the design of the supplementary HVAC-system are also important factors that need to be taken into account at an early stage in the design phase. To solve these interdisciplinary problems it requires a design team that can work together closely. The architect, and the engineer that is responsible for the energy performance of the building, have a central role to play at the very beginning of the design phase when the geometry and the general parameters of the building is still in flux.