User-friendly heating and ventilation systems for low energy and passivehouses

Status

finished

Summary

Part A

Motivation

The energy demand of new buildings has been decreased significantly during the last 25 years. This is due to the development of new building materials and building technology. Whereas 10 years ago common windows had a U-value of 3 W/(m²K) today's U-values are half of this at the same price. Similar developments have been achieved for other building materials which results in a specific energy demand of only one sixth (50 kWh/m²a) of today's buildings compared to buildings 30 years ago without additional costs. With little higher investment cost the energy demand can be decreased even further.

Low energy buildings (or passivehouses) have different demands for the heating systems than conventional buildings. This research project deals with these demands and an analysis of various heating systems with respect to end-use and primary energy demand, greenhouse relevant emissions, heat delivery costs (including capital costs) and qualitative criteria.

Content

Following a general introduction two passivehouses which were energetically monitored within the EC-project CEPHEUS were simulated in TRNSYS. The results were compared to the measurements and a sensitivity analysis of various parameters for the simulation compared to the measured room temperature course was undertaken.

A set of user behaviour patterns (ventilation, room temperature, presence, internal gains ..) was developed using a questionnaire in 53 apartments of low-energy multi family buildings, the measurements in the EC-project CEPHEUS, and an additional literature research. Using these data two reference multi family buildings, insulated according to passivehouse criteria, were set up for the simulation.

Following this, nine different heating systems for such buildings (4 air heating and 5 water heating systems) with the heat sources decentralized air/air/water heat pump, central ground coupled heat pump, central pellets or gas burner, and decentralized pellets or tiled stove were described and qualitatively analyzed.

Four out of these systems (decentralized air/air/water heat pump, centralized ground coupled brine/water heat pump, centralized gas- and pellets burner, all centralized systems using two-pipe heat distribution systems) were simulated in detail using the simulation tool TRNSYS. They were compared according to end-use and primary energy demand, CO2-equivalent emissions, heat delivery costs (including capital costs), and their sensitivity for changing user behaviour.
Additionally a sociological analysis using questionnaires and additional literature review was undertaken to evaluate the user demand and user acceptance for the various heating and heat delivery systems.

Aims of the project

The main goal was the development of a comprehensive evaluation method for heating systems for buildings insulated according to passivehouse criteria.

Methods used in the study

Questionnaire, measurements and literature review; evaluation using statistical methods, set up and use of simulation models using the tool TRNSYS.

Data used

Earlier projects in the frame of "Haus der Zukunft", EC- and other projects, own inquiries

Part B Results

Simulation of buildings insulated according to passive house criteria

It is possible to reach high accordance of the measured and simulated room air temperatures, when very detailed input data is available. Little differences i.e. in the user behaviour can alter the results significantly because the heat demand of the building is very small. An increase of the room set temperature from 20°C to 25°C increases, for example, the space heating energy demand by over 50% (with all other parameters fixed). For detailed simulations and comparisons the user behaviour taken from standards is not sufficient. Even user profiles evaluated from questionnaires are sometimes not accurate enough (this is especially true for the ventilation by windows).

Heating systems for buildings insulated according to passive house criteria

Heating systems for buildings insulated according to passive house criteria have to meet other requirements than heating systems for conventional buildings. Possible heat delivery systems are pure air heating systems (if the space heat demand for transmission and infiltration lays below 14 W/m²) as well as all kinds of water systems (radiator, floor-, and wall heating systems). The room-side temperatures of the windows and walls to the ambient are always relatively high in such well insulated buildings, which results in a good indoor climate. Nine different heating systems (space heating and domestic hot water) were described and analyzed qualitatively. One of the main results of the sociological questionnaire was, that in multi family buildings the type of the heating system is not seen as relevant as long as it works, is simple to be used, has no failures, and little maintenance costs. Problems with the acceptance occur for not optimal planned or mounted systems (dimensioning, control, noise etc.) no matter which type of system.

Simulation of the reference plants

The room temperature for the simulations was set to 22.5°C according to the results of the questionnaire. All systems apart from the central ground-coupled brine/water heat pump was additionally calculated with an incorporated solar thermal plant. The lowest energy demand could be found for the decentralized air/air/water heat pump system with solar thermal collectors, followed by the centralized ground-coupled brine/water heat pump equally to the decentralized air/air/water heat pump system without solar thermal system. The lowest greenhouse gas emissions were found for the centralized pellets system. The lowest heat delivery cost has the centralized gas-burner system without solar plant; the highest were found for the decentralized air/air/water heat pump system with solar thermal collectors. This system includes the controlled ventilations system, which would have to be paid separately for the other systems. The electricity demand of the building apart from the heating system is very relevant for the total primary energy demand. As this demand is not strongly coupled to the heating system, it was taken out of the newest calculations for passive houses in Germany. For "normal" user behaviour all systems can keep the desired room air temperature and humidity over the whole heating period. For extreme behaviour (high heat load due to high room air temperature and low internal gains and for the heating up after cooling down periods) the limited heating capacity of the air heating systems becomes visible. For heating up the floor heating system of the brine/water heat pump system reacts slower than the radiators, but the cooling needs also longer.

No significant difference could be found in the heating systems for the two reference buildings.

General conclusions

Generally all analyzed heating systems fulfil the user demands, therefore it cannot be said that there is a "winner". Each system has its own specifications and pros and cons and the total evaluation is depended on the type and the surrounding conditions of the building and the users. This report lists all the criteria and gives the user the opportunity to make his own decision.

Project manager

Prof. Dipl.-Ing. Dr. Wolfgang Streicher
Institute of Thermal Engineering , Graz University of Technology

Partners

Dipl.-Ing. Alexander Thür
AEE INTEC, Arbeitsgemeinschaft ERNEUERBARE ENERGIE, Institut für Nachhaltige Technologienf

Dipl.-Ing. Harald Rohracher
Inter-University Research Center for Technology, Work and Culture (IFZ)

Dipl.-Ing Arch. Helmut Krapmeier
Energieinstitut Vorarlberg, Dornbirn

Participating Companies:

Ing. Christof Drexel
Drexel und Weiss, Energieeffiziente Haustechniksysteme GmbH, Bregenz

Dipl.-Ing. Erwin Stubenschrott, Dipl.-Ing. Wilhelm Schmidt
KWB Kraft & Wärme aus Biomasse GmbH, St. Margarethen

Josef Steiner
Hexatherm Energietechnik GmbH, Ybbs an der Donau

Karl Hofer
Fa. Vaillant, Wien

Contact

Prof. Dipl.-Ing. Dr. Wolfgang Streicher
Institute of Thermal Engineering , Graz University of Technology
Inffeldgasse 25
A 8010 Graz
Tel.: +43 316 873-7306
Fax: +43 316 873-7305
E-Mail: w.streicher@tugraz.at