Bulletin of the Transilvania University of BraşovCIBv 2015 • Vol. 8 (57) Special Issue No. 1 - 2015

THE ASSESSMENT OF FLOWTEMPERATURE AND COATING LAYER

ON TABS PERFORMANCE

G. DRAGOMIR1 A.I. BREZEANU1 A. ȘERBAN G. NĂSTASE V. CIOFOAIA

Abstract: One of the newest heating and cooling system developed worldwide is Thermal Activated Building System. The efficiency of the radiantsurfaces, especially the TABS systems is influenced by the temperaturevariation over their surface. This is being influenced basically by the flowtemperature and the coating layer. This study through laboratory simulationand experimental measurements analyses the influence of these two factorson the functional performances of TABS.

Key words: TABS, assessment of flow temperature, coating layer.

1 Civil Engineering Faculty, Transilvania University of Braşov.

1. Introduction

The buildings are one of the majorenergy consumers and are responsible for asignificant amount of greenhouse gasemissions, which is, as is well known,responsible for climate change. From thethe total amount of energy used inbuildings, the thermal energy has thehighest influence, which is predominantlyproduced by burning fossil fuels, whichleads to significant emissions of carbondioxide (CO2) into the environment. Themain methods of reducing greenhousegases resulting from the process ofproducing thermal energy used inbuildings is represented by increasing thethermal insulation of buildings and use ofrenewable energy sources. The growinginterest, throughout the world, in theconcept of use for heating/cooling inindoor spaces renewable energy led to theuse of low temperature heat sources such

as soil, ground water, water from lakes etc.The most common method of extractingheat from these sources is the use of heatpumps witch operate with high efficiency,It is necessary that the temperaturedifference between the energy source andheating flow to be minimal.

The main method to ensure thermalcomfort in buildings in the tertiary sector,but not only, is to use complex ventilationand air conditioning, systems, which areusually associated with high primaryenergy consumption. This method has seena rapid spread in the second half of the lastcentury, when energy prices were verylow, and now with the constant increase inenergy price, this solution has become anirrational concept. [5].Due to thermal discomfort, sick-buildingsyndrome and excessive energyconsumption, the need to replace all or partof these systems and to develop new

Bulletin of the Transilvania University of Brasov• Vol. 8 (57) Special Issue No.1 - 2015334

concepts facilities for space heating andcooling for buildings, emerged.

Currently, the heating/cooling systemsrich close to the new trend (loweringenergy consumption), use of renewableenergy. Increase in thermal comfort can beachieved by using low temperature radiantsystems combined with ventilation systemsthat provide only the minimum flow offresh air to ensure the physiologicalcomfort [2].

Today, the trend for the residential andtertiary buildings is to use better insulation,better and lon glife materials for thepipeline (eg. PEXa) , improved systemcontrols, and wider use of renewableenergy sources. All of these led to awidespread use of radiant surfaces forthermal comfort, both during heating andcooling season.

According to the REHVA guideline[1].,-low temperature heating and hightemperature cooling, radiant surfaces weredivided into three categories, as shown inFigure 1:

1. Radiant cooling panels-RCP2.Water-based embedded surface cooling

systems-ESCS3. Thermally activated building systems-

TABS

Fig. 1. Radiant surfaces types

2. TABS

The envelope elements such as walls,floors, ceilings can be activated by using of

electric resistance, air or hydronic circuits.TABS are designed to integrate as part ofthe building structure and in its overallenergy strategy.

The modern concept of thermallyactivating the building mass wasconducted for the first time by Swissengineer Robert Meierhans, which togetherwith architect Peter Zumthor developedtwo successful projects, namely: Valsthermal baths in Switzerland (1996)(Meierhans and Olesen, 1999) and BregenzKunsthaus in Bregenz , Austria (1997) [6]and [7].

TABS are massive systems with highthermal capacity, having in this case a slowdynamic response to changes in cooling orheating loads. This feature, significantlydistinguishes them from other radiantsystems used to ensure thermal comfort inbuildings.

During dynamic operation of TABS,there are three distinct phases, namely: /disposal/receiving heat from the hydroniccircuit, storage and disposal/receiving heatto the environment. Receiving/disposal/heat from the hydronic circuit is achievedby pumping the flow through the pipelinesystem embedded in the constructionelements, which is a process that can becontrolled by means of temperature andmass flow of heat.

The main purpose of this control is thatthe TABS to accumulate enough energy tofuture operating conditions.

Thermal storage is achieved by thermallyactivating the building element. Because ofits high thermal massiveness, thesesystems will not only have a direct effectof heating/cooling, but will have the abilityto reduce the maximum thermal load andtransfer some of this during the vacancy ofthe building.

The heat transfer process of TABS fromthe environment is different from other airconditioning systems and is done both byconvection and radiation.

DRAGOMIR, G., et al.: The assessment of flow temperature and coating layer on TABS …. 335

3. Simulation

3.1. Simulation requirementsTo highlight the influence of the coating

of the radiant surface and flow temperatureon the functional performance of TABS wesimulated the steady state heat transfer.The simulation was done using COMSOLMultiphysics program, and Heat TransferModule. To solve the problems of heattransfer, the program uses a mathematicalstructure that is based on systems ofdifferential equations with partialderivatives. [8] [9].

TABS functional performancesimulation results was analyzed on a modelidentical to that designed and developed inthe laboratory of radiating surface of theFaculty of Civil Engineering TransilvaniaUniversity of Brasov.

3.2. The influence of the coating onthe functional performance of TABS

Depending on the roomsfunctionality, the floor coating varies fromceramic tiles to woven carpet witchdirectly influences the thermal properties.The type and properties of the material ofwhich the coating of the radiating surfacesignificantly influence both the surfacetemperature and the uniform heat flux.

The most common cases of floors areanalyzed below (tiles, PVC carpet, andwoven carpet floor) [3], their influencebeing directly proportional to thecoefficient of thermal conductivity of thematerial and its thickness, as shown in thefigure 2 and 3. The lower surface of TABSis most often covered only with a layer ofplaster, therefore it was not modified inthis study.

The influence of the topcoat onperformance of the lower radiating surfaceis insignificant [3].

Fig. 2. Temperature distribution fordifferent types of the coating layer, during

heating season

Fig. 3. Heat flux distribution for differenttypes of the coating layer, during heating

season

3.3. The influence of watertemperature on system functionalperformance of TABS

Water temperature is perhaps the mostimportant parameter influencing thethermal performance of the TABS. Theincrease in temperature value leads to asignificant increase in the averagetemperature of the radiating surface. Asshown in Figure 4. a temperature increaseof 15°C leads to an increase in theradiating surface temperature with 6°C. Atrelatively low temperatures of the waterflow the influence of the coating layer inthe TABS temperature is insignificant. Theincrease in water flow temperature resultsin the increase of the influence of thecoating layer.

Bulletin of the Transilvania University of Brasov• Vol. 8 (57) Special Issue No.1 - 2015336

Fig. 4. Average radiant surfacetemperature on the upper face of TABSsystem for different temperatures of the

heat flow

The increase in flow temperature from30ºC to 45ºC to lead to an increase ofabout 2.8 times the heat flow delivered tothe floor as you can see in the figure belowfig. 5.

Fig. 5. The heat distribution heat flowon the upper face of TABS

4. Laboratory Research

4.1. Experimental conditions

To study the influence of surface coatingand temperature on thermal performanceof TABS a series of experimentalmeasurements were conducted on theTABS existing surfaces in the. FacultyBuilding fig. 6. The radiating surface isdivided into four zones with differentlayers of coating on the radiating surface(tiles, parquet, carpet and PVC carpet).

Fig. 6. TABS radiant surface in thefaculty laboratory

The TABS in the laboratory has an areaof 6 m2 having a pipe coil made of PEXA20×2,2 mm diameter and 28 m length.

The laying pipe is in the form of doublecoil assembly having a 20 cm mountingpitch.

The concrete slab that containes the pipehas a thickness of 20 cm and the followingthermotehnic properties

KmW

×= 200,2l , 32600 m

kg=r

The schematic of the slab is presented infigure 7.

Fig. 7. Schematics of the TABS in theradiant surface laboratory

DRAGOMIR, G., et al.: The assessment of flow temperature and coating layer on TABS …. 337

The thermal agent is supplied to TABSfrom a manifold, type HKV-D, witch alsofeeds the othe radiant surfaces in thelaboratory [9].

The source for the thermal agent is a heatpump and an absorption chiller mountednear the faculty building of the Faculty.

Measurement and processing system forthe TABS is embedded in a complexsystem that monitors all radiant surfaces

and also the entire laboratory envelope.

4.2. Results

Measurement process results highlightedthe influence of two important parameters(water temperature and radiant surfacecoating) on the functional performance ofTABS

Fig. 8. Temperature on the radiant surface

Fig. 9. Heat flux delivered by the radiant surface

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Another important parameter is the heatflow from radiating surface. It variesdepending on water temperature and theindoor air between 20 and 100 W/m2, withlower values for the case using radialsurfaces covered with woven carpets, PVCcarpet and parquet.

5. Conclusion

TABS represent solutions for thermalcomfort in buildings which have thecapacity to provide heat for well insulatedbuildings.

The heat flow for TABS sites can reachvalues of up to 100-110 W/m2 for heattemperatures of up to 45ºC.

Radiant surface temperature and heatflux delivered to TABS is less influencedwhen using parquet, PVC carpet andsignificantly influenced by woven carpet.

The flow temperature is the designparameters that most influence the surfacetemperature and heat flux system deliveredto TABS.

References

1. Babiak, J., Olesen, B., Petras, D.: Lowtemperature heating and hightemperature cooling. REHVAGuidebook, Federation of EuropeanHeating ahd Air-ConditioningAssociations, 2007.

2. Dragomir, G.: Sisteme deîncălzire/răcire de joasa temperaturăutilizând enegia geotermală (Low

temperature radiation heating/cooling systems that use geothermalenergy) In: Ph.D. Thesis, TransilvaniaUniversity of Braşov, Braşov,Romania, 2015

3. Dragomir, G., Nastase, G., Ciofoaia,V., Boian, I., Serban, A., Brezeanu,A.: The impact of design parameterson the cooling performance of TABS,Bulletin of the TransilvaniaUniversity of Braşov • Vol. 7 (56) -Series I: Engineering Sciences 2014

4. Dragomir, G., Brezeanu, A., CiofoaiaV.: Experimental research on thetemperaure distribution of thermallyactivated building systems (TABS),Bulletin of the TransilvaniaUniversity of Braşov • Vol. 7 (56) -Series I: Engineering Sciences 2014

5. Ma, P., Wang, S. L., Guo, N.: Energystorage and heat extraction – Fromthermally activated building systems(TABS) to thermally homeostaticbuildings, Sustainable EnergyReviews 45(2015)677–685

6. Meierhans, R, Olesen, B. W.:Betonkernaktivierung. Germany:Velta Norderstedt; 1999.

7. Meierhans, R.: Room air conditioningby means of overnight cooling of theconcrete ceiling. ASHRAE Trans1996;V. 102(1):693–7 (AT-96-08-2).

8.*** Heat Transfer Module User´s Guide,Comsol

9.***http://www.comsol.com/comsol-multyphisics, Accessed: 22-10-2015.