Title of Contribution to ROOMVENT 2004

Thermal performance of a local bench heating system for churchesD. Limpens-Neilen 1 , M.E.A. Schoffelen 1 , H.L. Schellen 11 Eindhoven University of Technology, Department FAGO, Vertigo floor 6, P.O. Box 513, 5600 MB Eindhoven,The Netherlandsemail: d.neilen@bwk.tue.nl http://sts.bwk.tue.nl/friendlyheating/Summary: Within the European project “Friendly Heating” a local heating system is designed. The maingoal is not to heat the monumental churches themselves, in order to prevent damage to valuable art worksand the building itself. The idea is to provide a thermal comfort zone for the people in the pew usingradiant heat sources. Measurements in a climate room are used to a) evaluate the local climate created bythe bench heating system and b) evaluate the CFD model. The results will be used in ongoing research onthe prediction of the indoor climate in a church under real climate conditions.Keywords: local heating, measurements, CFD, thermal performanceSubject category: Indoor climate performance of buildings1 IntroductionThe problems of conservation, thermal comfortand the costs for heating in churches are still withouta common solution. Especially in churches that areused only once a week for liturgical celebrations, a lotof problems occur. In the first place, there areproblems concerning the conservation of the buildingand the artworks in it. Secondly, there is a problemwith the thermal comfort of the people. And there arealso the large costs for heating the church.When the church is heated, the heated air rises uptowards the vault, introducing a warm zone in theupper part of the church, while the area where thepeople are seated remains relatively cold. This meansthat there are large heating costs, while the people stillcomplain about the temperature being too low.From the point of view of limiting the heatingcosts, church boards prefer to heat the indoor airrapidly, which introduces abrupt variations in theindoor climate. These variations in temperature andrelative humidity (H) mostly are the main cause of theproblems with the conservation of artworks and otherinterior parts of monumental churches [1], [2].Within the European Project “Friendly Heating” anew heating system is being designed. This novelheating system is intended to provide people withthermal comfort and, at the same time, to avoid anyrisk on damaging artworks preserved in churches. It isa local bench heating system that provides the heatonly where it is needed. The case study for thisEuropean project is the church of Rocca Pietore in theItalian Dolomites where the prototype of the heatingsystem is installed [3].The main goal of this research is to study thethermal performance of the local heating system,regarding both conservation criteria and thermalcomfort. The first part of the research, which ispresented in this paper, is to perform referencemeasurements on the pews equipped with the heatingsystem in a climate room under steady conditions.The results of these measurements will be used forverification of the computer simulations on the sameclimate room set-up. The main question is how tomodel the local heating systems that are applied in thebenches. To answer this question, we must know theinfluence of heating system on the local climate in thepews, i.e. what changes in temperatures and airvelocities are introduced?Later on, the effect of the heating system on theoverall climate in a church can be investigated withregard to the conservation criteria.2 Local bench heating systemAs mentioned before, a local bench heating systemis applied in the church of Rocca Pietore, Italy. Thislocal system aims to warm the people in the pews,with a minimum influence on the rest of the church.For this goal, radiant heating is the most appropriatebecause the heat is radiated straight towards thepeople without a large effect on the environment. Butsimultaneous kinds of heat transfer (convection andconduction) should always be taken into account.The heating elements used in this research consistof two types of electrical heat sources: heating foiland resistance cables. The heating foil (Thermotex)consists of glass fabrics that are impregnated withelectrical conducting plastics "PTFE-Carbon". Tinplated copper foils are stitched to the edges of theheating foil as bus bars. The electrical insulation isobtained by laminating a compound of polyester/polyethylene foils. This heating foil, with a powersupply of 220V, is used in the elements that areapplied in the back and under the seat of the pew.Figure 1 shows the heating systems that areapplied in the pews.

sheet. The sheet is heated and then radiates to thewooden floorboard and the people’s feet that areplaced beneath the kneeler pad.Figure 1. Heating elements applied in the pew2.1 Seat heating elementBack heatingSeat heatingKneeler PadheatingThe heating element that is applied under the seatis a semicircular element, with heating foil as the heatsource, which is designed to radiate heat to people’slegs. In order to prevent overheating the seat, whichcan cause the wood to crack, insulation is appliedbehind the heating foil. So the heat is only radiated tothe wooden floorboard and to the front and back ofthe pew. In order to protect the heating foil, it iscovered with a perforated metal grid that is kept at adistance of 1 cm from the foil with help of spacers.The perforation rate of the metal grid is 50% so the IRradiation from the heating foil can reach the peopledirectly.In one pew, two of these heating elements areapplied, each with an electrical load of 155W. Thespecifications are presented in table 1.2.3 Back heating elementIn the back heating element, the heating foil iscovered on both sides (back and front) with theperforated metal grid that is mentioned before. Themetal grid in this heating element is also kept at adistance of 1 cm from the foil using spacers. Theheating element is attached between the back and theseat; in fact it closes the back of the pew.In each pew, one back heating element is appliedwith an electrical load of 370W.3 Climate room set-upThe measurements discussed in this paper wereused as input parameters for the boundary conditionsof the CFD model. Secondly, these results will beused for the verification of the simulation results.Eventually, the heating system that will be used in thechurch pews will consist of a combination of heatingelements. But to study the effects of each heatingelement on its environment, all measurements wereperformed on one type of heating element in a steadystate indoor environment. This environment wascomposed in the climate chamber of the EindhovenUniversity of Technology.2.2 Kneeler pad elementThe heating element that is applied beneath thekneeler pad consists of a resistance wire (RaychemElectromelt EM2-R) that is double folded. Theresistance of the wire increases when the temperatureof the wire increases. Therefore the wire has a peakload of 970W right after switching on the power anddecreases to 130W when the equilibrium temperatureis reached after about 3 minutes. To preventoverheating the kneeler pad, which can damage thewood, insulation is applied between the electricalresistance wire and the kneeler pad. This combinationof insulation and heating wire is covered with a metalFigure 2. Overview of climate room with the benchesTable 1. Overview of the heating systemsHeatingelementShape Protective cover ofthe elementHeat sourceseat semicircular metal grid,50% openback rectangular metal grid,50% openKneeler rectangular metal sheet Electricalpadresistance wireLength[m]Width[m]Height[m]ElectricalPower[W]#per pewElectrical foil 0.99 Radius = 0.11 155 2Electrical foil 2.00 0.02 0.35 370 12.00 0.09 0.02 130(start peak 970W)1

In this climate room - see figure 2 for thedimensions - a measurement set-up was built aroundthree church pews in which the local heating elementswere applied. The heating elements could be operatedseparately.The heating elements were turned on for 75minutes: it took 15 minutes for the system to heat up,after that the measurements continued for 60 minuteswhich is about the duration of a service. During thesemeasurements, the wall, ceiling and floortemperatures were kept at a temperature of around6°C. The idea behind this temperature was to createan indoor climate that represents the average indoorclimate of the church of Rocca Pietore in theDolomites (northern Italy) during winter.4 Measurement methods4.1 Infrared thermographyInfrared thermography is an appropriate method tomeasure surface temperatures, but not for measuringair temperatures. Because an impression of both airand surface temperatures was desired, paper stripswere fixed to the ceiling, which enabled us to measurethe temperature of the paper. This temperaturerepresents a combination of the local air temperatureand the radiant temperature. Due to its low heatcapacity, paper is suitable for this. Paper strips insteadof a paper plane are used in order to avoid extremedisturbance of the air movement.4.2 Local climateAt first, infrared thermographic pictures weretaken in the climate room. After that, smoke testswere performed to visualize the airflow around thebenches and the heating system. Those two kinds ofmeasurements gave a first impression of the influenceof the local heating system on the temperaturedistribution and air movements between the benches.Figure 3. Measurement grid applied in the plane cutThe positions of the temperature sensors as well as theair velocity sensors were determined on the basis ofthese measurements. The measurements on the localclimate at different locations in a plane cut wereperformed for each heating system. A measuring gridwas applied to this plane cut, see figure 3. (The blackplane is only applied for making the measuring gridvisible on the picture). The air temperature wasmeasured at 16 positions on the measuring grid usingNegative Temperature Coefficient (NTC) sensors.The surface temperature was also measured usingNTCs at 24 positions. Squirrel data loggers wereapplied to register the output of these sensors. AllNTCs were positioned in a way that the influence ofdirect radiation effects was minimized. The airvelocities and turbulence intensities were measuredusing hot sphere anemometers. A configuration thatwas made with a 3-channel Input Module and an A/Dconverter, allowed a simultaneous 10Hz samplingfrequency and storage of the bridge voltage output forall anemometers. The anemometers were placed at the8 most important positions, determined on the basis ofthe performed smoke tests. The hot sphereanemometers were calibrated using the calibrationmethod described by Loomans [4],[5].Figure 4. IR thermograph of the bench with the heatingsystem under the seat turned on.Figure 5. Air flow between the benches with the heatingsystem under the seat turned on.

Figure 6. Air and surface temperatures with seat andkneeler pad heating system operating6 CFD SimulationsThe set-up of the benches with the local heatingsystem in the climate room is modelled in the CFDpackage Fluent, version 6.1 [5]. In the simulationmodel the standard k-ε model is applied with thestandard wall functions. In this model a structural gridis applied with grid cells that grow from the areaaround the benches towards the boundaries of theroom. The room boundary conditions like wall,ceiling and floor surface temperatures as well as theinitial surface temperatures of the benches werederived from the measurements in the climate room.A first simulation of the seat heating system isperformed.6.1 EvaluationThe first simulation results were evaluated withhelp of the measurements discussed before. Thisevaluation showed that the surface temperatures of thebenches (see figure 6) were in good agreement withthe measurements (figure 4). These figures show thesame temperature distribution on the wooden benchesand the heating system.The next step in this research is to investigatewhat kind of viscous model should be used to achievean accurate CFD simulation of the local climatebetween and around the benches.The results of this evaluation will be used todetermine the parameters that are important as inputfor the simulations. First, this will be used forperforming simulations under the steady conditions ofthe climate room. In ongoing research, these resultswill be used for modelling and performing CFDsimulations of the situation in a church under realclimate conditions.7 ConclusionsFrom the measurements that have been performedin this research, the influence of the different heatingelements on the local climate in and around thebenches has become clear. The heating elementsunder the seat and in the back have the largestinfluence on this local climate. The air temperaturesbetween the benches increased up to 4°C, while atsome positions a maximum increase in surfacetemperatures of 10°C was measured. The mostimportant region of impact for air velocities is foundat shoulder height. The influence of the heatingelement under the kneeler pad is limited to the regionadjacent to this element.The first simulation results of the seat heatingsystem are in good agreement with the results of thesmoke tests and the infrared thermographic pictures,which give a general impression of airflows andtemperature distribution. For a more detailedverification, the temperatures and air velocitiesmeasured on the different positions can be used.In ongoing research this verification will beperformed for the two other heating systems. Afterthat, the model can be upgraded to the real situation inthe church building with the actual outdoor climateconditions.AcknowledgementsThe work presented in this paper is part of theEuropean project “Friendly Heating” which is fundedby the European Commission in the 5 th FrameworkProgram under contact no: EVK4-CT-2001-00067.The authors would like to acknowledge the financialsupport they have received from the EuropeanCommission.References[1] Schellen, H. L., 2002: Heating monumentalchurches: indoor climate and preservation ofcultural heritage. Dissertation EindhovenUniversity of Technology, The Netherlands.ISBN: 90-386-1556-6[2] Arendt, Claus, 1993: Raumklima in grossenhistorischen Raümen: Heizungsart,Heizungsweise, Schadensentwicklung,Schadensverhinderung. ISBN: 3-481-00564-4[3] www.isac.cnr.it/friendly-heating[4] Loomans, M.G.L.C, 1998: The measurement andsimulation of indoor airflow. DissertationEindhoven University of Technology, TheNetherlands. ISBN: 90-6814-085-X[5] Loomans, M.G.L.C.; Schijndel, A.W.M. van,1998: Simulation and measurement of thestationary and transient characteristics of the hotsphere anemometer. Eindhoven University ofTechnology, The Netherlands, FAGO report98.08.K[6] Fluent Inc., Fluent User’s Guide, version 6.1,Lebanon, USA, February 2003