Air conditioning of clear coin showcase

REHVA Journal – December 2011

Constantinos Maritsas

Sofia University, Bulgaria

kmar@abv.bg

Summary

The below study concerns the electromechanical installations theAir Conditioning of the Coin Exhibit Case so as the coins to be kept in an absolute clean environment, humidity and stable temperature. The Air Conditioning is achieved with inlet of warm or cold air at the Coin Exhibit Case through ducts from pipelines Æ15 mm/0.6 in that independent on automation, separate for each Coin Exhibit Case. The production of the clean air under the required pressure is realised by Medical Air Cylinders.

Introduction

The construction of the “Ilion Melathron” (the “TrojanMansion”) begun in 1870, a few years after Schliemann has settled into Athens. It was designed by his friend and compatriot Ernst Ziller. The mansion floors are tessellated which depict geometric motifs and representations of the artifacts coming from the excavations of the Mycenae and Troy. The wall and ceiling paintings are either exact copies of Pompeian themes or illustrations of Schliemann’s excavations and finds in the same style. As the residence of a distinguished archaeologist the “Ilion Melathron” housed the fruits of the labours of his remarkably adventurous life, as well as his dreams and his visions. It also housed amid publicity and splendour solitude and family tranquility, in the same area where the coins of Schliemann’s collection delighted the eyes of their possessor and the eyes of his select visitors.

Today the Numismatic Museum of Athens is one of the very few of this kind all over the world and the only one in Greece and the Balkans. Possessing about 600 000 coins which come from the ancient Hellenic world, the Roman era, Byzantium, the medieval European West and the modern times, as well as a great number of hoards, excavational finds, lead seals, medals and gems (acquired either by donations or by purchase), the Numismatic Museum, is called to preserve and secure these treasures and present them to the audience.

And here it comes this study to accomplish this task. The object of the study is the creation of a proper environment for the preservation and exhibition of the coins. In particular, the coins will be exhibited inside showcases, where will be, in parallel, preserved too. Consequently, the showcases must, on the one hand, permit the exhibition of the coins to the visitors of the Museum, and on the other hand, provide the proper conditions for the coins preservation. At the same time, the showcases must secure the coins against theft during the opening hours of the Museum, regardless of the general security system, which is “not operative” during the Museum’s opening hours. Each showcase has two compartments. In the upper compartment, will be placed the coins and it is airtight in the lower compartment, the air conditioning organs, the air ducts, the cables and everything its necessary, this part of the showcase is not airtight.

The object of the study is the creation of a proper environment for the preservation and exhibition of the coins. In particular, the coins will be exhibited inside showcases, where will be, in parallel, preserved too. The cause of the study is the design of a system of air-conditioning (heating, cooling, humidity, air filtering) and lighting of the showcases.In particular, the air-conditioning system must secure inside the show-cases the proper conditions for the preservation of the copper and metallic coins, namely:

·         temperature 21 +/–1°C (69.8 +/–1.8°F), without sudden changes;

·         humidity less than 25%, i.e. dry air, without sudden changes;

·         elimination of the atmosphere pollutants, i.e. ozone, sulphur oxide and nitric oxide, fume etc.

Problems

The place itself of the CoinMuseum is a "museum place", namely the floors bear mosaics, the walls are painted, the frames, the doors and windows etc. have been restored to their initial condition. Consequently, any intervention in the building elements is impossible resulting to the difficulty of connection of the showcases with the electricity, air-conditioning ducts networks etc.

The Museum is situated at the centre (most polluted) area of Athens and as it is known, the pollutants are the enemy number one of the museum exhibits. Consequently, the external air which will be used for the air-conditioning of the showcases, must be filtered not only from particles, fume etc. but also from chemical combinations, namely molecules. And the removal of molecules and smells by conventional bug filters or even by absolute filters 99.995% is impossible. Only activated carbon filters can eliminate the smells.

The areas of the Museum are not air-conditioned and as a result, the fluctuations of temperature and humidity are great. Therefore the air-conditioning of the showcases must offset the lack of air-conditioning of the surrounding areas.

Brief description of the proposed solution

All the showcases will be connected between them by a bar made of aluminium profile, achieving in that way the following:

·         support of the showcases;

·         creation of a control zone (prohibition) of the circulation behind the bar;

·         indication of the course of the visitors inside the Museum;

·         march inside the bar of the required cables and air-ducts for the electric power supply to and the air-conditioning of the showcases.Inside the bar two (2) air-ducts will proceed, one (1) with hot air (25°C/77°F) and one (1) with cold air (15°C/59°F).

·         With "T" junctions inside the bar, each showcase will be connected with both air-ducts. Through proper automatons, the showcase will be gated up or cooled, according to its internal temperature.

Analytical description of the air-conditioning installation

For the air-conditioning of the showcases compressed air will be used Medical Air Cylinders. The two (2) cylinders will be placed at the building' s engine-room.Apart from the two compressed air cylinders, the production centre will include:

·         an alternating-current generator for the alternation of the two compressed air cylinders;

·         a pressure eliminator 20 000/800 kPa (2 940/118 psi) with regulation of 300–500 kPa (44–73.5 psi);

·         a gate valve for the isolation of the cylinders;

·         metallic bracket for the cylinders.

The air after the pressure eliminator will have a temperature of approximately 15°C/59°F. Via a special "T" fitting, the air will be branched and one (1) branch will remain at 15°C/59°F. (cooling air) and the other branch will pass through a pot containing water at a stable temperature of 25°C/77°F, which is achieved by a thermostat and electric resistance, in order that its temperature may be increased at 25°C/77°F (heating air).In this way we succeed the following:

1)air heating and cooling with small  difference of temperature, so that no sudden alterations of the show-cases temperature be presented;

2)stable zero humidity of the air letting in the showcases, because the air of the cylinders is dry;

3)inlet of clean air without pollutants in the showcases;

4)possibility of use of gas nitrogen without control of the temperature when the whole Museum is air-conditioned;

5)economic operation with only consumable the compressed air cylinders;

6)simple installation without automatons, electrical consumption and maintenance by unskilled persons;

7)stable quality of the produced air during all the hours of operation

Figure 1.

The ducts network will proceed inside the bar and will be made of a flexible plastic pipeline Æ12 mm/0.45 in. Operation pressure of the network: 300–500 kPa (44–73.5 psi). The network will start from the building' s engine-room, where the cylinders will be installed, will proceed through the existing air-conditioning ducts and will end up at the ground-floor where it will be inserted in the show-cases connection bar (See Figure 1).The air-ducts network will proceed exclusively inside the bar.In the crossing through the frames, doors and windows, the air-ducts and the cables will proceed in the existing vacuum of the frames.As it was mentioned above, in each showcase both ducts will be inserted for heating and cooling respectively. The heating 21+/–1°C (69.8+/–1.8°F) and cooling of the showcase, for the achievement of a stable temperature of will be realized by air and with small difference of temperature, Dt=5°C/9°F so as no sudden changes of the temperature be created.In the entrance of the showcase the heating (cooling) air will have a pressure of 300–500 kPa (44–73.5 psi), therefore a pressure regulator will be placed, so that the pressure be reduced at 2 kPa/0.3 psi. After the pressure regulator the air will pass through an electro driven sluice valve "on-off" which is controlled by a thermostat adjusted at 20°C/68°F(22°C/71.6°F for cooling). When the temperature falls below 20°C/68°F (raises above 22°C/71.6°F), then the thermostat gives a signal and the hot (cold) air sluice valve opens (See Figure 2). When the temperature is restored to the desired level, the thermostat gives the proper order and the heating (cooling) sluice valve shuts. The expansion (ventilation) valve will be placed at the bottom of the airtight division of the showcase, permits the exit of the air when some sluice valve is open, so that the overpressure of the showcase be stable.All the organs, namely the pressure regulators, the electric sluice valves and thermostats are placed at the lower division of the showcase.The above-mentioned operation of the air-conditioning system attains:stable temperature, small changes of temperature, overpressure in the showcase, so that no air from the environment may enter, which carriers’ pollutants, humidity and dust.

Figure 2. Instruments under the exhibition boxes.

Calculations

In the present phase only approximate calculations will be made, which will justify the sizes of the air-ducts. In the phase of the application study, accurate calculations will be made. Given that many controlled factors affect the operation of the air-conditioning system, e.g. temperature of the Museum area etc. in the phase of construction there is the possibility of adjustment of the installation to the real operative conditions due to the pressure regulators in each show-case and in the beginning of the air-ducts.

Volume of show-case" V = 0.6 x 0.6 x 0.03 = 0.0108 m³ (1.97 x 1.97 x 0.1 =0.38 ft³)

Total volume: V = 40 x 0.0108 = 0.432 m³ (40 x 0.38 = 15.2 ft³)

With 6 alternations/hour of the air in the air-conditioning system we have a total supply of:

Q = 6 x 0.432 = 2.6 m³/h (6 x 15.2 = 91.5 ft³/h = 1.52 cfm.

With a velocity of approximately 10m/s (1970 fpm), which is usual for medical air installations, the following cross section of the air-duct results:

S = 2.6 m³/h/10 m/sec = 0.72 cm² (1.52 cfm/1970 fpm = 0.0008 ft²)or diameter:

d = (4 x S/p) = 10 mm/0.4 in. So, the choice 0.45 in is correct.