P French handling of alternative cooling techniques: free cooling and ground heat exchanger. [European projects]

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1 [European projecs] P H. LAHMIDI, CSTB, France More informaion can be found a he ASIEPI projec ebsie:.asiepi.eu Similar Informaion Papers on ASIEPI and/or oher European projecs can be found a he individual projec ebsies and in he publicaions daabase of he BUILD UP Poral:.buildup.eu French handling of alernaive cooling echniques: free cooling and ground hea exchanger There are a lo of alernaive cooling echniques ha improve subsanially he summer comfor ihou (or in a very limied manner) increasing he energy consumpion. For example solar and hermal conrol echniques, hea amorizaion and hea dissipaion echniques. Mos used echniques in France are free cooling in office buildings and ground hea exchanger in dellings. This paper focuses on providing general informaion describing he implemenaion of EN 1541 and EN 154 ino French regulaion o evaluae passive cooling based on venilaion. I conains an explanaion of he calculaion mehod ih deailed informaion on inpu and oupu daa. 1 > Handling of free cooling due o indos opening by implemening EN154 In he pas, buildings ere venilaed naurally. Wih an increased aareness of he cos and environmenal impacs of energy use, naural venilaion is again becoming an increasingly aracive echnique for reducing energy use and cos and for providing comforable indoor climae. During pracically all he summer period, he ouside air can be a source of coolness from evening o morning. So, in he case of a building ih an imporan ineria, a nigh over-venilaion enables he evacuaion of hea sored up in dayime. Figure 1 presens he effec of ineria for differen ypes of buildings in France. The EN 154 sandard describes he mehods o calculae venilaion airflos raes for buildings o be used in applicaions such as energy calculaions, heaing and cooling load calculaions, summer comfor and indoor air qualiy evaluaions. This sandard is implemened ino French regulaion for ne buildings called RT005. The mehod is mean o be applied o: Figure 1: Effec of ineria. all ypes of buildings; no direcly applicable o buildings ih a heigh greaer han 100 m or for rooms here he verical air emperaure difference is greaer han 15K; no applicable o ichens preparing food ha is no for immediae consumpion; no applicable o indusry process venilaion; auomaic indos opening are no considered by his sandard.

2 The inpu parameers and he calculaion mehod can be adjused or complemened for hese differen applicaions. Clause 7 of he sandard explains ha mus/can/should be aen ino accoun for each applicaion, and hich mehod should be used in each case. Three mehods are proposed in he sandard: 1 - Direc mehod The calculaion of mechanical airflos, combusion airflos and indo opening airflos, are all based on sysems characerisics, exernal condiions and design airflos. They do no depend on he inernal pressure condiion: he ineracion beeen he venilaion sysems and he leaages is negleced. - Ieraive mehod The ieraive mehod is required hen he ineracion beeen he venilaion sysems and he leaages canno be negleced. I is herefore proposed for passive duc venilaion. 3 - Saisical analysis for energy calculaion This mehod can be specified a he naional level for energy calculaions. The requiremens for he mehods are given in of he presen sandard. As described belo, he mehod proposed in he sandard, and folloed by French building regulaion o calculae air flo hrough opening indos area and boom hung indos are obained hrough he direc calculaion mehod (see: 6.5 of he presen sandard). I aes ino accoun: he ind urbulence; he ind speed; sac effec; he inside and ouside emperaure; user behaviour. For a single side impac, he airflo is calculaed by: V 0.5 q = vairing 1800* Ao * V = C + C.( V ) + C. H. abs( θ θ ) me s indo i e Wih: q v (m³/h): air flo; A (m²): indo opening area; C o = 0.01 aes ino accoun ind urbulence; C = aes ino accoun sac effec; s C = aes ino accoun ind speed; H V me indo (m): is he free area heigh of he indo; ( m / s) : meeorological ind speed a 10 m heigh; θ i : room air emperaure; θ : oudoor air emperaure. e ASIEPI > P185_French_Handling_of_Alernaive_Cooling_ASIEPI_WP7.doc

3 For a boom hung indo, he raio of he flo hrough he opened area and he oally opened indo is assumed o be depending only on he opening angle α and independen of he raio of he heigh o he idh of he indo. A = C (α ). A Where A is he indo area oally opened. o For C (α ), a polynomial approximaion is proposed in he sandard (see Figure ). In France, he opening area evolves linearly agains operaive emperaure inside he inerval θ op min =0 C andθ op max =4 C, ih: For θ θ, A 0 op < op min = For θ op > θ, A = op max A indo Cross venilaion is aen ino accoun hough consan values forc V ) (see Table 1)..( me Figure : A polynomial approximaion for C (α ) Table 1: Consan values. Cross venilaion 0.01 Venilaion C (α) depends on building ype, maximal opening, noise and ime. The values used in he French regulaion RT 005 are idenical for residenial and saniary buildings and are summarized in he able belo. Table : C (α ) values for residenial and saniary buildings. Noise s caegory From 8 p.m o 7 a.m From 7 p.m o 9 a.m From 9 a.m o 8 p.m BR BR For all oher building ypes, values are presened belo. Table 3: C (α ) values for oher building ypes. Noise s caegory Inoccupaion Occupaion BR BR To presen he effec of indos opening using his model, e performed a calculaion for a ypical French delling in Carpenras (See Figure 3). The useful surface of his building is 100 m² and he surface of indos is m². Resuls obained are summarized in Table 4. Figure 3: Sudied house. Table 4: Resuls of simulaions in Carpenras. Ineria C (α ) Maximum indoor emperaure ligh medium heavy ligh medium heavy ASIEPI > P185_French_Handling_of_Alernaive_Cooling_ASIEPI_WP7.doc 3

4 As expeced, o ensure comforable condiions, he maximal opening and a heavy ineria are he mos efficien combinaion. Figure 4: Principle of ground hea exchanger > Handling of ground hea exchanger by implemening EN1541 The earh remains much more cooler han he air in summer. This coolness can be used by means of earh cooling ubes (see Figure 4). These are underground ubes hrough hich venilaion air is circulaed. The venilaion air is hereby reheaed in iner and cooled don in summer. An earh cooling ube mus be correcly designed for beer efficiency and for easier mainenance in order o avoid any healh ris relaed o he qualiy of air. Annex A of his sandard describes a simplified model o calculae air precooling due o supplying air hrough ducs lying in he ground. The model calculaes: Figure 5: round emperaures for several duc dephs (X: annual hour, Y: Temperaures) leaving air emperaure of he hea exchanger; hea flux beeen ground and air in duc. The model aes ino consideraion he specific duc parameers and he ineria of he ground, depending on he deph of he ducs in he ground. Also he ground maerial is aen ino accoun by a correcion facor for he ground emperaure. This model ill be implemened ino he nex French regulaion scheduled for 01. In his model he ground emperaure depends on o parameers: he annual mean ouside emperaure; air emperaure and he deph of he ducs. The ground emperaure is modelled as a sinus curve based on he annual mean ouside air emperaure. The deph of ducs correcs he sinus curve in o ays: he ampliude decreases in funcion of he deph; he ground emperaure is rearded in funcion of he deph. I means he ineria of he ground increases in funcion of he deph. The ground emperaure depends on he annual mean and he ampliude of he annual sing of he ouside air emperaure a he building locaion, and on he deph of he duc in he ground (see Figure 5). To ae ino consideraion he ineria of he ground, he ouside air emperaure is correced by AH, VS and gm. AH correcs he ampliude, depending on he deph of he ducs lying in he ground. AH 3 = deph deph deph + 1 VS correcs he ground emperaure by a ime shif, depending on he deph of he ducs lying in he ground. VS = 4.( deph deph deph deph 4 ) ASIEPI > P185_French_Handling_of_Alernaive_Cooling_ASIEPI_WP7.doc 4

5 Table 5: gm values.. maerial gm Mois soil 1 Dray sand 0.9 Mois sand 0.98 Mois clay 1.04 We clay 1.05 Finally, he air ground emperaure is calculaed as follo: ih Δ sing. T TA π = gm. T AM AH. ΔTA.sin. VS [ JH + 4. ] being he ampliude of he annual ouside air emperaure Some gm values for soil maerials are proposed in his sandard (see Table 5). The leaving air emperaure is calculaed ih he formula: Figure 6: Poenial of hea ground exchanger in Nice during Augus ASIEPI parners: BBRI (BE; echnical co-ordinaor), NKUA (R; financial & adminisraive co-ordinaor), TNO (NL), IBP (DE), SINTEF (NO), CSTB (FR), Cee de Lyon (FR), REHVA (BE), ENEA (IT), AICIA (ES), NAPE (PL), VTT (FI), E-U-Z (DE), Enviros (CZ), SBi (DK) Associaed parners: Eurima (BE), PCE (BE), ES-SO (BE), EuroAce (BE), FIEC (BE), Acciona I (ES) Subconracors: Kaunas Universiy (LT), Universiy of Budapes (HU), Universiy of Buchares (RO), BRE (UK), UCD (IE) Lin:.asiepi.eu Wih: T AirOu = T ( T T U e : Transfer coefficien of he air duc Cp air : specific hea capaciy of air M air : Dry air mass flo rae AirIn U e. AS ). e M air. Cp Finally, he air ground emperaure and leaving air emperaure can be calculaed. Figure 6 presens an example of poenial of his echnique in he souh of France during Augus. The air oule from he duc is much cooler han exernal emperaure. 3 > Acnoledgemens Differen naional conribuions ere made by many of he projec parners. The parners are all lised on.asiepi.eu. 4 > References 1. EN 1541: Calculaion mehods for energy losses due o venilaion and infilraion in commercial buildings.. EN154 Calculaion mehods for he deerminaion of air flo raes in buildings including infilraion. air Original ex language: English Disclaimer: ASIEPI has received funding from he Communiy s Inelligen Energy Europe programme under he conrac EIE/07/169/SI The sole responsibiliy for he conen of his publicaion lies ih he auhors. I does no necessarily reflec he opinion of he European Communiies. Neiher he European Commission nor he auhors are responsible for any use ha may be made of he informaion conained herein. European Communiies, 009 Reproducion is auhorised provided he source is acnoledged ASIEPI > P185_French_Handling_of_Alernaive_Cooling_ASIEPI_WP7.doc 5