Prediction of Thermal Comfort and Ventilation Efficiency for Small and Large Enclosures by Combined Simulations

Institute for Thermodynamics and Building Energy Systems, Dresden University of Technology Prediction of Thermal Comfort and Ventilation Efficiency for Small and Large Enclosures by Combined Simulations I. Müller, A. Perschk, W. Richter and J. Seifert Basic criteria for heat transfer in enclosures Energy consumption Thermal comfort Hygienic comfort Summary/Outlook

Basic Criteria for heat transfer in enclosures Thermal Comfort Energy Consumption Hygienic Comfort 1. Energy Consumption: - based on the heat transfer process (convection / radiation) - technical equipment, thermal conditions of the enclosure 2. Thermal Comfort: - subjective sensation by individuals - Fanger-equation PMV / PPD Index (EN ISO 7730) 3. Hygienic Comfort: - depending on the air exchange - ventilation efficiency, age of the air, removal of contaminants TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 2

Calculation methods Calculation based on a coupled simulation of flow field and thermal behavior of the enclosure Thermal behavior of the enclosure: - special version of TRNSYS (TUD) - include a detailed procedure for the prediction of radiation - special types for simulation of technical equipment Simulation of the flow field: - ParallelNS (Finite Element Method) - research code (University of Göttingen / TU Dresden) - based on the Reynolds-averaged Navier - Stokes equations -k-ε turbulence model (with special wall treatment) TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 3

Part 1 Energy Consumption model represents a room in a low energy house one external wall with two windows, south orientation the adjacent rooms have the same geometry / same heating system TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 4

Part 1 Energy Consumption - Investigations over a period of 24 h - taking into account : weather conditions, internal gains Result: - differences between the models are important - detailed approximation of real conditions only with a coupled investigation TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 5

Part 2 Thermal Comfort Fanger- equation: PMV / PPD index completing criteria: draught risk, radiant temperature asymmetry, air speed, humidity Fig. Geometry of the room with possible heating systems Investigations: different levels of insulation, different heating systems, different air change rates TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 6

Part 2 Thermal Comfort heating case low energy house ac 0.25/h flow field, wall temperature - operative temperature, radiant temperature asymmetry TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 7

Part 2 Thermal Comfort- heating case low energy house draught risk for air change rates 0.0/h, 0.1/h (left) 0.25/h, 0.5/h (right) TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 8

Part 2 Thermal Comfort cooling case flow field, wall temperature - PMV, radiant temperature asymmetry TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 9

Part 2 Thermal Comfort large enclosures heating case Fig. Operative temperature in a hall (20m x 10m x 7m) with radiant heating panels TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 10

Part 3 - Hygienic Comfort Transport equation for the age of the air (see Sandberg, Awbi, Roos) τ with : t Air exchange efficiency steady state p D r + ( u o ) τ o ( D τ ) = 1 p τ, e p ν ν : = +, Sc = Sc = 1.0 Sc Sc t τ, e τ τ, t (Reference value: nominal time constant) 2 τ τ, t ε a = τ n τ Air exchange efficiency transient ε a th, 1 V = V& t (Reference value: flow rate of a perfect displacement flow with the same mean age of the air) TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 11

Part 3 - Hygienic Comfort Academic test configuration Outdoor temperature 3.75 C Natural ventilation (window airing with working radiator) Y X Z 4 m 2.5 m 5 m Room 4m x 5m x 2.5m with window and radiator Completely open window, calm outside Geometrically modelled radiator, with periodically increasing/decreasing heat flux. /W Q W 400 350 300 250 200 150 100 50 0 0 600 1200 1800 2400 3000 3600 t/s TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 12

Part 3 - Hygienic Comfort Y Y Z X Z X Unsteady flow field with both effects: - Short circuit flow (left) and - Actual air change (right) ϑ / o C 12.0 11.3 10.6 9.9 9.2 8.5 7.8 7.1 6.4 5.7 5.0 Use of steady state evaluation criteria yields to unrealistic tendencies Hygienic air change rate predictable λ /h -1 10 9 8 7 6 5 4 3 2 1 λ λ hyg 0 0 600 1200 1800 2400 3000 3600 t/s ε a t ; εa t,h 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 ε a t ε a t,h 0 0 600 1200 1800 2400 3000 3600 t/s TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 13

Part 3 - Hygienic Comfort visualization of the age of air TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 14

Summary/Outlook Assuming reliable prediction of the flow field, several investigations can be carried out by combined simulations Working principles and efficiency of heating and cooling systems can be clearly demonstarted Improvements on the flow field calculation and turbulence modelling Transport of contaminants and humidity (building physics) TU Dresden EUROMECH colloqium 471, Oct. 13th-14th 2005, DLR Göttingen 15