New principles for air curtains design for high efficiency.

Air Curtains has become a standard way of protecting the doorway opening. Air Curtains has become a standard way of protecting the doorway opening. Although air curtains are used for many applications, mostly, they are used for temperature separation of the air volumes in the vicinity of the open doorway. Although air curtains are used for many applications, mostly, they are used for temperature separation of the air volumes in the vicinity of the open doorway. Nevertheless, today I will show that the thermal protection provided by air curtains is insufficient. This is not because air curtains are made by manufacturers improperly or because physical principles employed in air curtains do not work. This is because those principles have limitations, which lead to a lack of efficiency of air curtains. Nevertheless, today I will show that the thermal protection provided by air curtains is insufficient. This is not because air curtains are made by manufacturers improperly or because physical principles employed in air curtains do not work. This is because those principles have limitations, which lead to a lack of efficiency of air curtains.

AIR CURTAIN – OPERATION PRINCIPLE. EFFICIENCY. Unacceptable heat loss values take place even in the optimal conventional air curtain. place even in the optimal conventional air curtain.

Power which is loosing at the opening because of the temperature difference on the sides of the opening is given by the formula : W 0 = K·w·H 3/2 ·(ΔТ) 3/2, W 0 = K·w·H 3/2 ·(ΔТ) 3/2, w – width, Н – height, ΔТ – temperature difference, K ≈ 0,1

The efficiency of the device e may be defined as part of the thermal power which leakage was prevented by the operation of this device. W min = (1- e)·K·w·H 3/2 ·(ΔТ) 3/2 W min = (1- e)·K·w·H 3/2 ·(ΔТ) 3/2

What is the maximum possible value of the effectiveness e in air curtains?

In the article [A.M. Foster, M.J. Swain, R. Barrett, P. D'Agaro, L.P. Ketteringham, S.J. James. Three-dimensional effects of an air curtain used to restrict cold room infiltration. Applied Mathematical modeling, 31(6) , 2007.] In the article [A.M. Foster, M.J. Swain, R. Barrett, P. D'Agaro, L.P. Ketteringham, S.J. James. Three-dimensional effects of an air curtain used to restrict cold room infiltration. Applied Mathematical modeling, 31(6) , 2007.] Maximum effficiency is estimated as 71%. By the data [Gregory Verhaeghe, Arnout Willockx, Marnix Van Belleghem, Michel De Paepe. Study of air curtains used to restrict infiltration into refrigerated rooms. Heat Trasfer. Fluid Mechanics and Thermodynamics. By the data [Gregory Verhaeghe, Arnout Willockx, Marnix Van Belleghem, Michel De Paepe. Study of air curtains used to restrict infiltration into refrigerated rooms. Heat Trasfer. Fluid Mechanics and Thermodynamics. 7 th International Conference. Proceedings.(2010) pp ], 7 th International Conference. Proceedings.(2010) pp ], Maximum effficiency is estimated as 80%.

What parameters define the efficiency of the air curtain?

Efficiency as the function of initial air speed Air Air speed speed 4,25 m/s 4,25 m/s 6,75 m/s 6,75 m/s 14,0 m/s 14,0 m/s Initial width of the nozzle 5 sm, heating power of air curtain 2,5kW, additional power 2,5 kW Tout = -10°C, Tin=20°C, H=2м, t = 180 s

Real values of heat flux I propose to compare the heat losses through the three types of structures, the facade area of 3x3m, window area and an opening which is protected by an air curtain. Assume that all three areas are of the same size 3x3 meters and are used for the same values of Tin = C of the inside temperature and Tout = C of outside temperature. For values R of the thermal resistance of the facade and windows Regulation of gives the recommended values R for the Moscow climate. Let us calculate the heat loss as square footage times temperature difference divided by the value of thermal resistance. Heat losses for open aperture is calculated by the proposed formulas above with the lowest value of K = 0,06 and the maximum efficiency of the air curtain 80%. I propose to compare the heat losses through the three types of structures, the facade area of 3x3m, window area and an opening which is protected by an air curtain. Assume that all three areas are of the same size 3x3 meters and are used for the same values of Tin = C of the inside temperature and Tout = C of outside temperature. For values R of the thermal resistance of the facade and windows Regulation of gives the recommended values R for the Moscow climate. Let us calculate the heat loss as square footage times temperature difference divided by the value of thermal resistance. Heat losses for open aperture is calculated by the proposed formulas above with the lowest value of K = 0,06 and the maximum efficiency of the air curtain 80%.

Real values of heat flux. W wall = 85 Wт, W wall = 85 Wт, W win = 500 W, W win = 500 W, W ac ≈ W, W ac ≈ W, W 0 ≈ W W 0 ≈ W 1% enhancement of the air curtain efficiency can save about 1% enhancement of the air curtain efficiency can save about W W.

Значимость задачи уменьшения теплопотери. This huge difference in cost can be interpreted in this way This huge difference in cost can be interpreted in this way 1m 2 of the doorway protected by the high performance air curtain of the door in terms of heat loss can be compared with the heat loss through 60 m2 of the windows or through 375 m2 of the facade. 1m 2 of the doorway protected by the high performance air curtain of the door in terms of heat loss can be compared with the heat loss through 60 m2 of the windows or through 375 m2 of the facade. From the different point of view every percent of increase in the efficiency of the air curtain, which is mounted at 3x3 opening will result in savings of heat of the same value that is lost through the window construction area of about 30m 2 or facade area of approximately 170m 2. From the different point of view every percent of increase in the efficiency of the air curtain, which is mounted at 3x3 opening will result in savings of heat of the same value that is lost through the window construction area of about 30m 2 or facade area of approximately 170m

Why heating of air is needed at air curtain? 1. The compensation of heat loss. 1. The compensation of heat loss. 2. Imitation of the heating system (Secondary heating system). 2. Imitation of the heating system (Secondary heating system). 3. Creating a comfort zone for people in the opening of the doorway. 3. Creating a comfort zone for people in the opening of the doorway.

Efficiency of the air curtain with heating. Efficiency of the air curtain with heating. Why air curtain with heating of air steam has so low efficiency? Because the main part of the power doesn’t go into the room. I propose simple model of this phenomenon. I propose simple model of this phenomenon. W = 2kW/m 2 W = 2kW/m C C C C C C C C W 1 = W 2 = 1kW/m 2 W 1 ? W 2 ? W 1 = W 2 = 1kW/m 2 W 1 ? W 2 ?

Efficiency of the air curtain with heating. Efficiency of the air curtain with heating. Why air curtain with heating of air steam has so low efficiency? Because the main part of the power doesn’t go into the room. I propose simple model of this phenomenon. I propose simple model of this phenomenon. W = 2kW/m 2 W = 2kW/m C C C Тст ≈ 30 0 C C C C C Тст ≈ 30 0 C C W 1 = W 2 = 1kW/m 2 W 1 ≈ 0,4 kW/m 2 W 2 ≈ 1,6 kW/m 2 W 1 = W 2 = 1kW/m 2 W 1 ≈ 0,4 kW/m 2 W 2 ≈ 1,6 kW/m 2

How the efficiency of the air curtain without heating can be increased sufficiently? If we consider formula of heat loss for protected by air curtain opening W ac = (1- e)·K·w·H 3/2 ·(ΔT) 3/2 W ac = (1- e)·K·w·H 3/2 ·(ΔT) 3/2 Which of the variables in that formula could be changed for lowering of W?

How the efficiency of the air curtain without heating can be increased sufficiently? If we consider formula of heat loss for protected by air curtain opening W ac = (1- e)·K·w·H 3/2 ·(ΔT) 3/2 W ac = (1- e)·K·w·H 3/2 ·(ΔT) 3/2 We could change only the variable ΔT

How the efficiency of the air curtain without heating can be increased sufficiently? W min = (1- e)·K·w·H 3/2 ·(ΔT) 3/2 W min = (1- e)·K·w·H 3/2 ·(ΔT) 3/2: ΔT T ≈ (Tw+Tc)/2 ΔT T ≈ (Tw+Tc)/2 ΔT/2 ΔT/2 ΔT/2 ΔT/2 W 0,35W !!! W 0,35W !!!

Under what conditions we can use appoximation of average temperature? Criterion of approximation possibility использования of average Criterion of approximation possibility использования of average temperature T is L ≈ H temperature T is L ≈ H We can modify this scheme Then it can be used in compact construction of air curtain For this case we can For this case we can suppose, α ≈ 1 suppose, α ≈ 1 (α – an angle between 2 air jets) (α – an angle between 2 air jets)

For air curtain with heating. There is additional limitation. We can not heat external jet which is close to outside air. Heating the outside air stream would reduce the effectiveness of the entire scheme. But we can use heating at the inner jet!

Calculation in 2D model of ε – k turbulence. Conventional single jet air Conventional single jet air curtain. Heating power curtain. Heating power 5kW T av = 19,87 0 C. 5kW T av = 19,87 0 C. Double jet air curtain Double jet air curtain Heating power 2 kW Heating power 2 kW 40% T 1 = 19,09 0 C 40% T 1 = 19,09 0 C T 2 = 18,92 0 C T 2 = 18,92 0 C Double jet air curtain Double jet air curtain Heating power 2,5 kW Вт Heating power 2,5 kW Вт 50% T 1 = 23,21 0 C 50% T 1 = 23,21 0 C T 2 = 20,62 0 C T 2 = 20,62 0 C Double jet air curtain with only 43% heating power allows gaining the same or better conditions as the standard single jet curtain with 100% heating!

So, how do you ensure the comfort for people passing in the flow of the outer jet? If you surely do not have to heat outer jet If you surely do not have to heat outer jet

For this purpose I propose now an entirely new principle of heating the outer jet (objects inside it) with an infrared heater I also suggest a name for this principle IR DOOR as the analogue of the North American name for air curtain AIR DOOR While using this principle the importance is only in the personal feeling of comfort, not in the absolute values of energy flow.