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Application of an integrated indoor climate, HVAC and showcase model for the indoor climate performance of a museum
Energy and Buildings 40 (2008) 647–653 www.elsevier.com/locate/enbuild
Application of an integrated indoor climate, HVAC and showcase model for the indoor climate performance of a museum A.W.M. van Schijndel *, H.L. Schellen, J.L. Wijffelaars, K. van Zundert Technische Universiteit Eindhoven, Department of Building and Architecture, Building Physics and Systems (BPS), VRT 6.29, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Received 31 January 2007; received in revised form 26 April 2007; accepted 30 April 2007
Abstract This paper presents a case study on the performance based design of a HVAC system and controller of a museum. A famous museum in The Netherlands has reported possible damage to important preserved wallpaper fragments. The paper provides an evaluation of the current indoor climate by measurements, showing that the indoor climate performance does not satisfy the requirements for the preservation of old paper. To solve this problem we developed an integrated heat air and moisture (HAM) model consisting of models for respectively: the indoor climate, the HVAC system and controller and a showcase. The presented models are validated by a comparison of simulation and measurement results. The integrated model is used for the evaluation of a new HVAC controller design and the use of a showcase. It is concluded that it is not possible to satisfy the indoor climate within the recommended limits, exclusively by the use of a new control strategy. Furthermore in order to meet the recommendations, the wallpaper fragments should be placed in a showcase and a similar control strategy as presented in the paper, has to be implemented in order to limit the room air temperature change. # 2007 Elsevier B.V. All rights reserved. Keywords: Modeling; Heat air and moisture; HAM; MatLab; Buildings; Systems
1. Introduction In general, the aim of museums is to exhibit artifacts in its original state as long as possible. The climate performance surrounding the preserved artifact is of great importance. Furthermore, if present, the heating, ventilation and airconditioning (HVAC) system plays a dominant role on the indoor climate. A famous museum in The Netherlands has reported possible damage to important preserved wallpaper fragments. Preliminary measurements indicate that the indoor climate performance does not meet the criteria for preservation of wallpaper. A solution is sought-after, given that the current HVAC system cannot be replaced (only small modifications are possible) and that the use of showcases, although not prohibited, is not preferred by the decision makers. This leads to the next questions: first, what are the recommendations for the indoor climate concerning the preservation of (wall) paper? Second, is it possible to improve the indoor climate
* Corresponding author. Tel.: +31 40 247 29 57; fax: +31 40 243 85 95. E-mail address: [email protected] (A.W.M. van Schijndel). 0378-7788/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2007.04.021
performance, by a new control strategy of the current HVAC system, in such a way, that a showcase can be avoided? Third, if not, can the problem be solved by using a showcase? Due to the preservation of the object, measurement is not an option to answer these key questions because it is not allowed to experiment with the HVAC system. Therefore simulation is the only option and an integrated indoor climate, HVAC and showcase model is needed. There is no such a model available. This leads to two more questions: Fourth, can we develop an integrated heat air and moisture (HAM)/HVAC system model capable of predicting the current indoor climate and the climate in a showcase? Finally (fifth), can we improve the climate surrounding the object, using this model? The aim of the paper is to investigate the five mentioned questions. The following methodology was used: (1) reviews on the indoor climate criteria for preservation of wallpaper and on integrated indoor climate, HVAC and showcase models have been carried out. (2) The current indoor climate and HVAC performances were extensively measured. Data, measured by others, have been obtained for validating the showcase model. (3) Indoor climate, HVAC and showcase models were developed and validated. (4) An integrated model has been developed for the simulation of
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climate conditions near the object in case of a new HVAC controller design, with and without the use of a showcase. The outline of the paper is as follows: Section 2 presents review results on the optimal climate for the preservation of the object and the measured results of the actual indoor climate performance. Section 3 provides HAM models of the indoor climate, HVAC system and showcase and validation of the developed HAM models. Section 4 presents simulation results of new designs. Finally in Section 5, the key questions will be revisited and discussed. 2. The current indoor climate performance 2.1. Review on climate recommendations for (wall) paper We reviewed several recommendations for the preservation of paper from literature. A short summary of this review is presented now. Appelbaum [2] recommends a relative humidity (RH) between 40 and 50%. LCM Foundation [3] presents the next criteria for paper: (1) a RH between 48 and 55%; (2) a RH variation less than 3% per day; (3) an air temperature (Ta) between 16 and 18 8C; (4) a Ta variation less than 2 8C/h. Jutte [4] recommends a RH between 48 and 55%. Henne [5] and Johnson and Horgan [6] both present criteria on storage conditions for paper. Their recommendations are almost the same: a RH between 45 and 60% and a mean Ta of 20 8C. Furthermore Wijffelaars and Zundert [1] discussed their review results with an expert on paper preservation. They all concluded that the LCM Foundation [3] provided the best recommendations for the preservation of the wallpaper. We continue using recommendations (1)–(4). The next section presents the actual indoor climate conditions surrounding the wallpaper.
Fig. 1. The geometry of the room and constructions details.
if we could fix this problem, i.e. that the climate would be within the recommended area, the problem with the variations would probably also be fixed. As mentioned before, simulation is in our case the only option to study possible solutions of this problem. The next section presents the used heat, air and moisture (HAM) models. 3. HAM modeling and validation 3.1. Building, systems and controller
2.2. Measurements
All models are developed using HAMLab [7,8]. The main components and the input/output structure of the models are presented in Fig. 3.
We start with a short description of the situation. All important paper fragments are fixed at several walls in a single room. The window is orientated northeast. The room is permanently filled with about 10–20 persons during museum opening times. Information on the HVAC system is provided in Section 3. Fig. 1 provides some information on the geometry and constructions. The measurements were carried out from June 2003 through February 2004. They include: (1) the Ta, RH, solar irradiance and rainfall of the external climate; (2) the Ta and RH at several places in the room and surrounding rooms; (3) the Ta, RH and mass flow of the air inflow to the rooms. Fig. 2 presents the indoor climate conditions of the room that contains the wallpapers. We used a Mollier frequency plot for the visualization of the measured indoor climate. It is very clear that the indoor climate does not satisfy the recommendations, because 100% of the measured values are outside the recommended area (!). Furthermore, we checked whether the Ta and RH variation met the recommendations of respectively 2 8C/h and 3% per day. The measurements indicated that the Ta variation was within the recommendation but the RH variation was also out of limits. We identified the climate conditions surrounding the wallpaper as the main problem. We argued that
Fig. 2. The Mollier frequency plot of the measured indoor climate for June 2003 through February 2004. The grey area shows the percentage of time for each state to occur (scale see the bar on the right hand side). Summation of the whole colored area equals 100%. In blue the recommended area is provided. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
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Fig. 3. The input/output structure of the models. Labels: (1) measured time series: external climate (Te, RHe); solar irradiation (Qsolar); number of visitors; indoor climate (Tairmeas, RHairmeas). (2) The HVAC and controller model: input: simulated indoor climate (Tair, RHair) and external climate (Te, RHe); output: heat flow (QHVAC) due to heating or cooling and moisture flow (gHVAC) due to ventilation. (3) Room model (input and output are already specified). (4) Graphics block.
The HVAC system controller is modeled using the current control strategy for the exhaust air temperature of the HVAC system (equals the incoming air temperature of the room) Ta and a constant airflow of 1000 m3/h. The set point for Ta is a function of the outdoor temperature (Te) and indoor RH: 20 ðT e þ 10Þ T a ¼ max 17; 3 ðRH 40Þ þ min 10; (1) 2:5 The first part of (1) is a feed forward controller for heating and cooling with Te as parameter: the incoming air temperature Ta ranges from 20 8C (for Te = 10) to 17 8C (for Te 17 8C). The second part of (1) is a feed back controller with the indoor air RH as parameter: The Ta is raised 2 8C for every 5% RH above the 40% with a maximum of 10 8C. The latter provides some humidistatically control. The room is modeled as a single zone. The model parameters include realistic dimensions and material properties of the walls and the window presented in Fig. 1 and Table 1. After completing the models with the necessary data for the external climate and internal heat and moisture sources from visitors, the model of Fig. 3 was validated by measurements. Fig. 4 shows that the results are quite satisfactory. 3.2. The showcase modeling We developed a HAM model for a showcase. The model will be discussed now. Fig. 5 introduces the modeled quantities in relation with the location at the showcase and wallpaper board
inside it. Table 2 provides additional information on the used materials. The heat related model equations are based on a straight forward network of thermal resistances. The moisture related model equations are more complicated and therefore presented (2): dm3 m3 ¼ bRH ps ðT 3 Þ RH4 ; dt m3max ðT 3 Þ dm4 m3 ¼ þbRH ps ðT 3 Þ RH4 dt m3max ðT 3 Þ d ps ðT 4 Þ ðRH4 RH5 Þ md d RH4 d ps ðT 4 ÞðT 4 T 5 Þ ; md dm5 m6 ¼ þbRH ps ðT 5 Þ RH5 dt m3max ðT 6 Þ d ps ðT 4 Þ ðRH4 RH5 Þ þ md d RH 4 d ps ðT 4 ÞðT 4 T 5 Þ ; þ md dm6 m6 ¼ bRH ps ðT 5 Þ RH5 dt m3max ðT 6 Þ
(2)
where m is the water vapor mass, T the temperature, mmax(T) the maximum water vapor mass at temperature T, RH the relative humidity, bRH the surface coefficient of vapor transfer, d the vapor permeability coefficient, md the vapor diffusion thickness of paper, ps(T) the vapor saturation pressure at temperature T, and dps(T) the air saturation pressure derivative at temperature
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Table 1 Model parameters Category Zone Walls External (1)
Window
External (2)
Internal (3 and 4) Internal (5 and 6) Floor Ceiling Visitor
Parameter Volume Internal surface resistances External surface resistances Orientation Surface Materials (start inside) Surface Solar gain factor U-value Orientation Surface Materials (start inside) Surface Materials (start inside) Surface Materials (start inside) Surface Materials (start inside) Surface Materials (start inside) Heat source Moisture source
Value(s)
Ref.
3
27.7 m Heat: 0.13 W/m2 K; moisture Lewis relation Heat: 0.04 W/m2 K; moisture Lewis relation NE 5.4 m 2 0.01 m plaster; 0.2 m brick 1.9 m2; 0.25 5.6 W/m2 K SE 6.5 m 2 0.02 m wood; 0.35 m air gap; 0.2 m brick 7.2 m 2 0.02 m wood; 0.07 m air gap; 0.2 m brick 18.9 m 2 0.02 m wood; 0.07 m air gap; 0.02 m wood 10.1 m 2 0.003 m linoleum; 0.022 m wood 10.1 m 2 0.022 m wood 60 W 41 g/h
[2.6; 2.4]
[2.8; –; 2.4] [2.8; –; 2.4] [2.8] [2.23; 2.8]
The material properties of IEA Annex 24 report Volume 3 (1996) are used (Ref. refers to corresponding material section(s) of this report).
T. Subscripts 3–6 are the corresponding locations presented in Fig. 5. The showcase model was validated with data, measured by others. Unfortunately these data did not contain measured RH
values inside the showcase. Therefore only the thermal part of the model is validated (see Fig. 6). The moisture part of the model is verified by checking the mass balances in steady state.
Fig. 4. Validation results: air temperature (top), relative humidity (middle) and vapor pressure (bottom).
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Table 2 Additional information of the used materials for the showcase and inside Category
Parameter
Value(s)
Zone
Volume (l w h) Air Board Internal surface resistances Surface Material Materials (start inside) Surface Material
1.640 m 1.390 m 0.020 m 51% 49% Heat: 0.13 W/m2 K; moisture Lewis relation 2.28 m 2 0.006 m glass 0.003 m aluminum; 0.03 m insulation 2.25 m 2 0.01 m fiber board
Walls Front Other five Board
4. Simulation results of new designs
4.1. A new HVAC controller strategy without showcase
The models of the previous section are integrated into a single model in HAMLab. This model is used as a tool to simulate the design options mentioned in Section 1.
As mentioned before, it is not allowed to install new hardware ((de)-humidification) to the current HVAC system. Only modifications of the control strategy are possible. A feed back control of the Ta, using a set point of 18 8C, is suggested as possible improvement of the current control strategy, described by Eq. (1). Fig. 7 shows the new control model. Fig. 8 presents the simulation results. As expected the temperature is within the limitations of the control strategy. However, it is clear that the indoor climate still does not satisfy the recommendations. First, from the Mollier frequency plot, it is concluded that 92% of the measured values are outside the recommended area. Second, from the variations analysis, it is concluded that only the Ta changes are within the recommendations now. Third, the RH change per day is still out of limits. The problem we are facing now, is caused by the high moisture gains due to a high number of people inside the room. Without adding (de)-humidification sections to the HVAC system, this problem cannot be solved. As mentioned before such modifications are not allowed and therefore we proceed with the next design option. 4.2. The current HVAC system with a showcase
Fig. 5. The location of the modeled quantities: temperature (T) and relative humidity (w; RH) at the showcase and wallpaper board inside it (see sub labels): (1) interface room–glass; (2) interface glass–inside air; (3 and 6) inside air; (4 and 5) interface wallpaper board–inside air; (7) interface wall–inside air; (8) interface room–wall.
The previous results show that the use of a showcase is almost inevitable. Fig. 9 provides the simulations results of the climate in the showcase if the showcase model is subjected to the current climate conditions of room. Fig. 9 shows (as expected) a stable specific humidity inside a
Fig. 6. Validation results for the air temperature inside the showcase.
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Fig. 7. The new controller model (feedback).
Fig. 8. Mollier frequency plot of the simulated climate in the room (see Fig. 2 for explanation. Note: scales are different). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
Fig. 10. Mollier frequency plot of the simulated climate in the showcase (see Fig. 2 for explanation. Note: scales are different). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
4.3. A new HVAC controller with a showcase Fig. 10 provides the simulated climate in the showcase if the control strategy of Section 4.1 for the indoor climate of the room is used. Again, inside the showcase we expect a stable specific humidity. Furthermore, we also expect a stable air temperature inside the showcase because the air temperature in the room is much more stable now. Fig. 10 shows that the indoor climate inside the showcase almost satisfies the recommendations. If the set point is lowered from 18 to 17.5 8C, a perfect climate arises in the showcase for the preservation of wallpaper. 5. Conclusions
Fig. 9. Mollier frequency plot of the simulated climate in the showcase (see Fig. 2 for explanation. Note: scales are different). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
showcase. However, the climate in the showcase still does not satisfy the recommendations. This is mainly caused by the large range of indoor air temperature. Also the RH change per day inside the showcase is still out of limits. The problem is still not solved.
If we revisit the key questions mentioned in the introduction, we come to the next conclusions: (1) recommendations for the climate conditions concerning the preservation of (wall) paper are given. (2) An integrated indoor climate, HVAC system and showcase HAM model has been developed and validated. It is used to simulate the climate conditions for the different design options. (3) It is not possible to satisfy the indoor climate within the recommended limits, exclusively by the use of a new control strategy. Either (de-)humidification sections are needed in the HVAC system, which is not an option here, or the wallpaper fragments have to be placed in a showcase. (4) In order to meet the recommendations, the wallpaper fragments should be placed in a showcase and a similar control strategy as
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presented in this paper, has to be implemented in order to limit the room air temperature change. Acknowledgements The contribution of Marcel van Aarle to this work is greatly acknowledged by the authors. Furthermore, The Netherlands Institute for Cultural Heritage is acknowledged for providing measured data concerning the showcase validation. References [1] J.L. Wijffelaars, K. Zundert, Investigation on the indoor climate and wallpaper of a museum, Master Thesis 04.32.W Technische Universiteit Eindhoven, 2004 (in Dutch).
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[2] B. Appelbaum, Guide to Environmental Protection of Collections, Sound View Press, Madison, CT, 1991. [3] LCM Foundation, Syllabus for a Short Course on Preventive Conservation, 2002 (in Dutch). [4] B.A.G.H. Jutte, Passive Conservation, The Netherlands Institute for Cultural Heritage, Internal Report, 1994 (in Dutch). [5] E. Henne, Luftbefeuchtung, ISBN: 3486262890, 1995. [6] E.V. Johnson, J.C. Horgan, Protection of the Cultural Heritage; Technical Handbooks for Museums and Monuments 2, UNESCO, 1979. [7] M.H. de Wit, HAMBase, Heat, Air and Moisture Model for Building and Systems Evaluation, Bouwstenen 100, ISBN: 90-6814-601-7, Eindhoven University of Technology, 2006. [8] A.W.M. van Schijndel, Integrated Heat Air and Moisture Modeling and Simulation, Bouwstenen 116, ISBN: 90-6814-604-1, Eindhoven University of Technology, 2007.
Application of an integrated indoor climate, HVAC and showcase model for the indoor climate performance of a museum A.W.M. van Schijndel *, H.L. Schellen, J.L. Wijffelaars, K. van Zundert Technische Universiteit Eindhoven, Department of Building and Architecture, Building Physics and Systems (BPS), VRT 6.29, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Received 31 January 2007; received in revised form 26 April 2007; accepted 30 April 2007
Abstract This paper presents a case study on the performance based design of a HVAC system and controller of a museum. A famous museum in The Netherlands has reported possible damage to important preserved wallpaper fragments. The paper provides an evaluation of the current indoor climate by measurements, showing that the indoor climate performance does not satisfy the requirements for the preservation of old paper. To solve this problem we developed an integrated heat air and moisture (HAM) model consisting of models for respectively: the indoor climate, the HVAC system and controller and a showcase. The presented models are validated by a comparison of simulation and measurement results. The integrated model is used for the evaluation of a new HVAC controller design and the use of a showcase. It is concluded that it is not possible to satisfy the indoor climate within the recommended limits, exclusively by the use of a new control strategy. Furthermore in order to meet the recommendations, the wallpaper fragments should be placed in a showcase and a similar control strategy as presented in the paper, has to be implemented in order to limit the room air temperature change. # 2007 Elsevier B.V. All rights reserved. Keywords: Modeling; Heat air and moisture; HAM; MatLab; Buildings; Systems
1. Introduction In general, the aim of museums is to exhibit artifacts in its original state as long as possible. The climate performance surrounding the preserved artifact is of great importance. Furthermore, if present, the heating, ventilation and airconditioning (HVAC) system plays a dominant role on the indoor climate. A famous museum in The Netherlands has reported possible damage to important preserved wallpaper fragments. Preliminary measurements indicate that the indoor climate performance does not meet the criteria for preservation of wallpaper. A solution is sought-after, given that the current HVAC system cannot be replaced (only small modifications are possible) and that the use of showcases, although not prohibited, is not preferred by the decision makers. This leads to the next questions: first, what are the recommendations for the indoor climate concerning the preservation of (wall) paper? Second, is it possible to improve the indoor climate
* Corresponding author. Tel.: +31 40 247 29 57; fax: +31 40 243 85 95. E-mail address: [email protected] (A.W.M. van Schijndel). 0378-7788/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2007.04.021
performance, by a new control strategy of the current HVAC system, in such a way, that a showcase can be avoided? Third, if not, can the problem be solved by using a showcase? Due to the preservation of the object, measurement is not an option to answer these key questions because it is not allowed to experiment with the HVAC system. Therefore simulation is the only option and an integrated indoor climate, HVAC and showcase model is needed. There is no such a model available. This leads to two more questions: Fourth, can we develop an integrated heat air and moisture (HAM)/HVAC system model capable of predicting the current indoor climate and the climate in a showcase? Finally (fifth), can we improve the climate surrounding the object, using this model? The aim of the paper is to investigate the five mentioned questions. The following methodology was used: (1) reviews on the indoor climate criteria for preservation of wallpaper and on integrated indoor climate, HVAC and showcase models have been carried out. (2) The current indoor climate and HVAC performances were extensively measured. Data, measured by others, have been obtained for validating the showcase model. (3) Indoor climate, HVAC and showcase models were developed and validated. (4) An integrated model has been developed for the simulation of
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climate conditions near the object in case of a new HVAC controller design, with and without the use of a showcase. The outline of the paper is as follows: Section 2 presents review results on the optimal climate for the preservation of the object and the measured results of the actual indoor climate performance. Section 3 provides HAM models of the indoor climate, HVAC system and showcase and validation of the developed HAM models. Section 4 presents simulation results of new designs. Finally in Section 5, the key questions will be revisited and discussed. 2. The current indoor climate performance 2.1. Review on climate recommendations for (wall) paper We reviewed several recommendations for the preservation of paper from literature. A short summary of this review is presented now. Appelbaum [2] recommends a relative humidity (RH) between 40 and 50%. LCM Foundation [3] presents the next criteria for paper: (1) a RH between 48 and 55%; (2) a RH variation less than 3% per day; (3) an air temperature (Ta) between 16 and 18 8C; (4) a Ta variation less than 2 8C/h. Jutte [4] recommends a RH between 48 and 55%. Henne [5] and Johnson and Horgan [6] both present criteria on storage conditions for paper. Their recommendations are almost the same: a RH between 45 and 60% and a mean Ta of 20 8C. Furthermore Wijffelaars and Zundert [1] discussed their review results with an expert on paper preservation. They all concluded that the LCM Foundation [3] provided the best recommendations for the preservation of the wallpaper. We continue using recommendations (1)–(4). The next section presents the actual indoor climate conditions surrounding the wallpaper.
Fig. 1. The geometry of the room and constructions details.
if we could fix this problem, i.e. that the climate would be within the recommended area, the problem with the variations would probably also be fixed. As mentioned before, simulation is in our case the only option to study possible solutions of this problem. The next section presents the used heat, air and moisture (HAM) models. 3. HAM modeling and validation 3.1. Building, systems and controller
2.2. Measurements
All models are developed using HAMLab [7,8]. The main components and the input/output structure of the models are presented in Fig. 3.
We start with a short description of the situation. All important paper fragments are fixed at several walls in a single room. The window is orientated northeast. The room is permanently filled with about 10–20 persons during museum opening times. Information on the HVAC system is provided in Section 3. Fig. 1 provides some information on the geometry and constructions. The measurements were carried out from June 2003 through February 2004. They include: (1) the Ta, RH, solar irradiance and rainfall of the external climate; (2) the Ta and RH at several places in the room and surrounding rooms; (3) the Ta, RH and mass flow of the air inflow to the rooms. Fig. 2 presents the indoor climate conditions of the room that contains the wallpapers. We used a Mollier frequency plot for the visualization of the measured indoor climate. It is very clear that the indoor climate does not satisfy the recommendations, because 100% of the measured values are outside the recommended area (!). Furthermore, we checked whether the Ta and RH variation met the recommendations of respectively 2 8C/h and 3% per day. The measurements indicated that the Ta variation was within the recommendation but the RH variation was also out of limits. We identified the climate conditions surrounding the wallpaper as the main problem. We argued that
Fig. 2. The Mollier frequency plot of the measured indoor climate for June 2003 through February 2004. The grey area shows the percentage of time for each state to occur (scale see the bar on the right hand side). Summation of the whole colored area equals 100%. In blue the recommended area is provided. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
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Fig. 3. The input/output structure of the models. Labels: (1) measured time series: external climate (Te, RHe); solar irradiation (Qsolar); number of visitors; indoor climate (Tairmeas, RHairmeas). (2) The HVAC and controller model: input: simulated indoor climate (Tair, RHair) and external climate (Te, RHe); output: heat flow (QHVAC) due to heating or cooling and moisture flow (gHVAC) due to ventilation. (3) Room model (input and output are already specified). (4) Graphics block.
The HVAC system controller is modeled using the current control strategy for the exhaust air temperature of the HVAC system (equals the incoming air temperature of the room) Ta and a constant airflow of 1000 m3/h. The set point for Ta is a function of the outdoor temperature (Te) and indoor RH: 20 ðT e þ 10Þ T a ¼ max 17; 3 ðRH 40Þ þ min 10; (1) 2:5 The first part of (1) is a feed forward controller for heating and cooling with Te as parameter: the incoming air temperature Ta ranges from 20 8C (for Te = 10) to 17 8C (for Te 17 8C). The second part of (1) is a feed back controller with the indoor air RH as parameter: The Ta is raised 2 8C for every 5% RH above the 40% with a maximum of 10 8C. The latter provides some humidistatically control. The room is modeled as a single zone. The model parameters include realistic dimensions and material properties of the walls and the window presented in Fig. 1 and Table 1. After completing the models with the necessary data for the external climate and internal heat and moisture sources from visitors, the model of Fig. 3 was validated by measurements. Fig. 4 shows that the results are quite satisfactory. 3.2. The showcase modeling We developed a HAM model for a showcase. The model will be discussed now. Fig. 5 introduces the modeled quantities in relation with the location at the showcase and wallpaper board
inside it. Table 2 provides additional information on the used materials. The heat related model equations are based on a straight forward network of thermal resistances. The moisture related model equations are more complicated and therefore presented (2): dm3 m3 ¼ bRH ps ðT 3 Þ RH4 ; dt m3max ðT 3 Þ dm4 m3 ¼ þbRH ps ðT 3 Þ RH4 dt m3max ðT 3 Þ d ps ðT 4 Þ ðRH4 RH5 Þ md d RH4 d ps ðT 4 ÞðT 4 T 5 Þ ; md dm5 m6 ¼ þbRH ps ðT 5 Þ RH5 dt m3max ðT 6 Þ d ps ðT 4 Þ ðRH4 RH5 Þ þ md d RH 4 d ps ðT 4 ÞðT 4 T 5 Þ ; þ md dm6 m6 ¼ bRH ps ðT 5 Þ RH5 dt m3max ðT 6 Þ
(2)
where m is the water vapor mass, T the temperature, mmax(T) the maximum water vapor mass at temperature T, RH the relative humidity, bRH the surface coefficient of vapor transfer, d the vapor permeability coefficient, md the vapor diffusion thickness of paper, ps(T) the vapor saturation pressure at temperature T, and dps(T) the air saturation pressure derivative at temperature
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Table 1 Model parameters Category Zone Walls External (1)
Window
External (2)
Internal (3 and 4) Internal (5 and 6) Floor Ceiling Visitor
Parameter Volume Internal surface resistances External surface resistances Orientation Surface Materials (start inside) Surface Solar gain factor U-value Orientation Surface Materials (start inside) Surface Materials (start inside) Surface Materials (start inside) Surface Materials (start inside) Surface Materials (start inside) Heat source Moisture source
Value(s)
Ref.
3
27.7 m Heat: 0.13 W/m2 K; moisture Lewis relation Heat: 0.04 W/m2 K; moisture Lewis relation NE 5.4 m 2 0.01 m plaster; 0.2 m brick 1.9 m2; 0.25 5.6 W/m2 K SE 6.5 m 2 0.02 m wood; 0.35 m air gap; 0.2 m brick 7.2 m 2 0.02 m wood; 0.07 m air gap; 0.2 m brick 18.9 m 2 0.02 m wood; 0.07 m air gap; 0.02 m wood 10.1 m 2 0.003 m linoleum; 0.022 m wood 10.1 m 2 0.022 m wood 60 W 41 g/h
[2.6; 2.4]
[2.8; –; 2.4] [2.8; –; 2.4] [2.8] [2.23; 2.8]
The material properties of IEA Annex 24 report Volume 3 (1996) are used (Ref. refers to corresponding material section(s) of this report).
T. Subscripts 3–6 are the corresponding locations presented in Fig. 5. The showcase model was validated with data, measured by others. Unfortunately these data did not contain measured RH
values inside the showcase. Therefore only the thermal part of the model is validated (see Fig. 6). The moisture part of the model is verified by checking the mass balances in steady state.
Fig. 4. Validation results: air temperature (top), relative humidity (middle) and vapor pressure (bottom).
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Table 2 Additional information of the used materials for the showcase and inside Category
Parameter
Value(s)
Zone
Volume (l w h) Air Board Internal surface resistances Surface Material Materials (start inside) Surface Material
1.640 m 1.390 m 0.020 m 51% 49% Heat: 0.13 W/m2 K; moisture Lewis relation 2.28 m 2 0.006 m glass 0.003 m aluminum; 0.03 m insulation 2.25 m 2 0.01 m fiber board
Walls Front Other five Board
4. Simulation results of new designs
4.1. A new HVAC controller strategy without showcase
The models of the previous section are integrated into a single model in HAMLab. This model is used as a tool to simulate the design options mentioned in Section 1.
As mentioned before, it is not allowed to install new hardware ((de)-humidification) to the current HVAC system. Only modifications of the control strategy are possible. A feed back control of the Ta, using a set point of 18 8C, is suggested as possible improvement of the current control strategy, described by Eq. (1). Fig. 7 shows the new control model. Fig. 8 presents the simulation results. As expected the temperature is within the limitations of the control strategy. However, it is clear that the indoor climate still does not satisfy the recommendations. First, from the Mollier frequency plot, it is concluded that 92% of the measured values are outside the recommended area. Second, from the variations analysis, it is concluded that only the Ta changes are within the recommendations now. Third, the RH change per day is still out of limits. The problem we are facing now, is caused by the high moisture gains due to a high number of people inside the room. Without adding (de)-humidification sections to the HVAC system, this problem cannot be solved. As mentioned before such modifications are not allowed and therefore we proceed with the next design option. 4.2. The current HVAC system with a showcase
Fig. 5. The location of the modeled quantities: temperature (T) and relative humidity (w; RH) at the showcase and wallpaper board inside it (see sub labels): (1) interface room–glass; (2) interface glass–inside air; (3 and 6) inside air; (4 and 5) interface wallpaper board–inside air; (7) interface wall–inside air; (8) interface room–wall.
The previous results show that the use of a showcase is almost inevitable. Fig. 9 provides the simulations results of the climate in the showcase if the showcase model is subjected to the current climate conditions of room. Fig. 9 shows (as expected) a stable specific humidity inside a
Fig. 6. Validation results for the air temperature inside the showcase.
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Fig. 7. The new controller model (feedback).
Fig. 8. Mollier frequency plot of the simulated climate in the room (see Fig. 2 for explanation. Note: scales are different). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
Fig. 10. Mollier frequency plot of the simulated climate in the showcase (see Fig. 2 for explanation. Note: scales are different). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
4.3. A new HVAC controller with a showcase Fig. 10 provides the simulated climate in the showcase if the control strategy of Section 4.1 for the indoor climate of the room is used. Again, inside the showcase we expect a stable specific humidity. Furthermore, we also expect a stable air temperature inside the showcase because the air temperature in the room is much more stable now. Fig. 10 shows that the indoor climate inside the showcase almost satisfies the recommendations. If the set point is lowered from 18 to 17.5 8C, a perfect climate arises in the showcase for the preservation of wallpaper. 5. Conclusions
Fig. 9. Mollier frequency plot of the simulated climate in the showcase (see Fig. 2 for explanation. Note: scales are different). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
showcase. However, the climate in the showcase still does not satisfy the recommendations. This is mainly caused by the large range of indoor air temperature. Also the RH change per day inside the showcase is still out of limits. The problem is still not solved.
If we revisit the key questions mentioned in the introduction, we come to the next conclusions: (1) recommendations for the climate conditions concerning the preservation of (wall) paper are given. (2) An integrated indoor climate, HVAC system and showcase HAM model has been developed and validated. It is used to simulate the climate conditions for the different design options. (3) It is not possible to satisfy the indoor climate within the recommended limits, exclusively by the use of a new control strategy. Either (de-)humidification sections are needed in the HVAC system, which is not an option here, or the wallpaper fragments have to be placed in a showcase. (4) In order to meet the recommendations, the wallpaper fragments should be placed in a showcase and a similar control strategy as
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presented in this paper, has to be implemented in order to limit the room air temperature change. Acknowledgements The contribution of Marcel van Aarle to this work is greatly acknowledged by the authors. Furthermore, The Netherlands Institute for Cultural Heritage is acknowledged for providing measured data concerning the showcase validation. References [1] J.L. Wijffelaars, K. Zundert, Investigation on the indoor climate and wallpaper of a museum, Master Thesis 04.32.W Technische Universiteit Eindhoven, 2004 (in Dutch).
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[2] B. Appelbaum, Guide to Environmental Protection of Collections, Sound View Press, Madison, CT, 1991. [3] LCM Foundation, Syllabus for a Short Course on Preventive Conservation, 2002 (in Dutch). [4] B.A.G.H. Jutte, Passive Conservation, The Netherlands Institute for Cultural Heritage, Internal Report, 1994 (in Dutch). [5] E. Henne, Luftbefeuchtung, ISBN: 3486262890, 1995. [6] E.V. Johnson, J.C. Horgan, Protection of the Cultural Heritage; Technical Handbooks for Museums and Monuments 2, UNESCO, 1979. [7] M.H. de Wit, HAMBase, Heat, Air and Moisture Model for Building and Systems Evaluation, Bouwstenen 100, ISBN: 90-6814-601-7, Eindhoven University of Technology, 2006. [8] A.W.M. van Schijndel, Integrated Heat Air and Moisture Modeling and Simulation, Bouwstenen 116, ISBN: 90-6814-604-1, Eindhoven University of Technology, 2007.