Department store bathrooms with air conditioning have to think about 2 at the same time to suck out odors and moisture.

For department store bathrooms that are in air-conditioned zones, you have to think about 2 at the same time. 1. Ventilation fan / Exhaust Fan to suck out odors and moisture. 2. Size of air conditioner / Cooling Load because the air that is sucked out. There must be new air or Transfer Air coming in instead, causing a cooling load. The main principle is that the bathroom should have a slight negative pressure. To prevent the smell from flowing out into the mall zone 1) System concept used in air-conditioned mall restrooms, format…

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For department store bathrooms that are in air-conditioned zones, 2 must be thought about at the same time.
1. Ventilation fan / Exhaust Fan to suck out odors and moisture.
2. Air conditioner size / Cooling Load because of the air that is sucked out. There must be new air or Transfer Air to replace it, causing a cooling load.
The main rule of thumb is that the bathroom should be slightly negative pressure. In order to prevent the smell from flowing out into the department store zone.
1) System concept used in air-conditioned department store bathrooms.
General format:
Cool air from the air conditioner / Supply Air → Bathroom → Exhaust Fan is sucked out of the building.
and give
Exhaust Air > Supply Air
To keep the bathroom negative pressure
Example of Balance:
Item Air volume
Exhaust Fan 1,000 CFM
Supply Air from air conditioner 750–850 CFM
Transfer Air from the mall hall 150–250 CFM
This way, the smell won't push out of the bathroom. But it will be sucked into the bathroom and then drained.

2) How to calculate the exhaust fan size
for public restrooms Many standards base ventilation on the number of toilets, such as 50–70 CFM per toilet or urinal. The value is more or less depending on the usage and operation of the fan, such as Continuous or Intermittent.

Method 1: Calculate according to the number of sanitary ware.
Exhaust CFM = Number of Toilet × 50 to 70 CFM
For a department store with a lot of people using it, we recommend starting at
70 CFM / Fixture
Or at least check against ACH again.

The 2 method: Think according to ACH
Formula:
CFM = Room Volume × ACH / 1.699
where
* Room Volume = Area × Height, unit m³
* ACH = Air Change per Hour
* 1 CFM ≈ 1.699 m³/h
Basic values for department store restrooms:
Bathroom type ACH basic introduction
General bathroom 10–12 ACH
Department store bathroom / lots of people using it 12–15 ACH
Bathroom with strong smell / heavy use 15–20 ACH
The real work is to calculate both 2 methods and choose the larger value.

3) Exhaust Fan size calculation example
Suppose a department store bathroom has the following information:
* Bathroom area = 60 m²
* Ceiling height = 2.70 m
* Room volume = 60 × 2.70 = 162 m³
* Integrated sanitary ware
* WC = 8 set
* Urinal = 4 series
* Included = 12 Fixtures

Method 1: Think according to Fixture
Use 70 CFM / Fixture
Exhaust = 12 × 70
Exhaust = 840 CFM

The 2 method: Think according to ACH
Choose 12 ACH for department store bathrooms.
CFM = 162 × 12 / 1.699
CFM ≈ 1,144 CFM

Summary of fan selection
Compare:
Method Air volume
According to Fixture 840 CFM
According to ACH 1,144 CFM
Choose a value greater than and for the system:
Select Exhaust Fan ≈ 1,200 CFM
If you have a long air pipe, several elbows, a Fire Damper, Backdraft Damper, Louver, or Filter, you should allow for Static Pressure such as
Exhaust Fan 1,200 CFM @ 150–250 Pa

4) How to calculate the size of an air conditioner for an air-conditioned bathroom.
Loaded bathroom air conditioner has 2 main parts:

1. Room Load
such as walls, fire, people, equipment, accumulated heat
2. Ventilation / Exhaust Makeup Load
It is the burden from the wind that has been sucked out and new wind must come in to replace it.
For bathrooms in department stores The point to be careful of is a lot of exhaust air if the design is not good. The air conditioner must handle a higher load than expected.

5) Case 1: Makeup Air comes directly from outside air.
In this case, the air load will be very high. Because the hot and humid air outside has to be cooled and dried.
Approximate formula:
Cooling Load = 4.5 × CFM × Δh
The unit is BTU/h.
where
* CFM = new air volume
* Δh = Enthalpy difference between outside air and room air, unit BTU/lb.
for Bangkok The outside air may be approximately 35°C DB / 28°C WB.
Bathroom needs approximately 25°C, RH 55–60%.
Approximately, Δh may be around 12–14 BTU/lb.

Example
Exhaust = 1,200 CFM
If using Outside Air, fill it all up.
Assume Δh = 13 BTU/lb.
Cooling Load = 4.5 × 1,200 × 13
Cooling Load = 70,200 BTU/h
Convert to TR:
TR = 70,200 / 12,000
TR ≈ 5.85 TR
Therefore, if you take Fresh Air outside to fill it. 1,200 CFM The air conditioner must be used approximately.
6 TR
This is why mall restrooms should not directly bring in raw outside air without passing through OAU / PAU / DOAS.

6) In the case that 2: Makeup Air comes from a department store hall that is already air conditioned.
This is the more often used method.
The idea is to let some of the air from the air-conditioned shopping hall area pass through the transfer port or the space under the door and then exhaust it out.
In this case, the main Fresh Air load will go to the mall's AHU/OAU system, not the entire bathroom air conditioner.
Air Balance example:
Item Air volume
Exhaust Fan 1,200 CFM
Supply Air into WC 900 CFM
Transfer Air from Mall 300 CFM

The bathroom is also a negative because
Exhaust 1,200 CFM > Supply 900 CFM
The difference 300 CFM will be sucked from the mall hall into the bathroom.

7) Calculate the size of the bathroom air conditioner in a practical way.
For restrooms in department stores, if most of the Makeup Air is cool air from the mall hall then The size of the air conditioner in the bathroom is usually calculated from:
Cooling Load in the bathroom = Area Load + People Load + Lighting Load + the portion of Fresh Air/Transfer Load that must actually be received
Quick for Preliminary:
Description Default
Bathroom with general air conditioner 500–700 BTU/h·m²
Department store bathrooms use a lot 700–900 BTU/h·m²
Bathrooms that have a lot of hot Fresh Air coming in must be calculated from Enthalpy.

Example of calculating the size of an air conditioner
Bathroom area = 60 m²
Use preliminary value = 700 BTU/h·m²
Cooling Load = 60 × 700
Cooling Load = 42,000 BTU/h
Convert to TR:
TR = 42,000 / 12,000
TR = 3.5 TR
Therefore, choose an air conditioner approximately
4 TR
or approximately 48,000 BTU/h
But you must also look at Air Balance. If you have to supply air to the 900 CFM 4 TR air conditioner, you may need to check whether the machine can supply enough air or not. Because generally the air conditioner will have wind of about:
350–450 CFM/TR
If you choose 4 TR:
Supply Air ≈ 4 × 400 = 1,600 CFM
Sufficient to supply air 900 CFM, but must adjust the Damper and should not supply too much air until the bathroom becomes positive pressure.

😎 Summary of equipment selection examples
From the example of a department store bathroom:
* Area = 60 m²
* Height = 2.7 m
* Fixture = 12 set
* Requires a room with negative pressure.

Exhaust Fan
Choose from ACH approximately 1,144 CFM
For the system
Select Exhaust Fan = 1,200 CFM @ 150–250 Pa

Air Conditioning
In the case of Makeup Air coming from an air-conditioned department store hall:
Choose an air conditioner approximately 4 TR or 48,000 BTU/h.
Air supply to WC approximately:
850–950 CFM
Then let the transfer air from the mall hall increase approximately:
250–350 CFM

Recommended Air Balance
List of design fees
Exhaust Air 1,200 CFM
Supply Air from air conditioner 900 CFM
Transfer Air from the mall hall 300 CFM
Negative Pressure Room Status

9) Transfer Air channel size
If you want Transfer Air = 300 CFM
Convert to m³/s:
300 CFM × 0.000472 = 0.142 m³/s
If the wind speed is set through the Transfer box, approximately 1.5 m/s.
Free Area = 0.142 / 1.5
Free Area ≈ 0.095 m²
If using a Louver with Free Area 50%
Gross Area = 0.095 / 0.5
Gross Area ≈ 0.19 m²
such as approx size
400 × 500 mm
or close to it and look at the Free Area from the actual Catalog again.

10) Design precautions
* Do not let Supply Air be more than Exhaust because the smell will push out into the shopping hall.
* Should not return air from the bathroom back into the central AHU.
* Exhaust should be thrown out of the building. Shouldn't let it get into the ceiling.
* Exhaust suction point should be near the toilet bowl / odor area / above.
* There should be an access door for cleaning the fan and air ducts.
* If there is a very long pipe, the actual Static Pressure must be calculated.
* If you want to save energy, you may use Heat Recovery with Exhaust, but you must be careful of leakage of odor contamination back into the system.

Easy to remember formula
Fan size
Exhaust CFM = Select maximum value from
* Fixture × 50–70 CFM
* Room Volume × ACH / 1.699
Air conditioner size
If Fresh Air comes directly from outside:
BTU/h = 4.5 × CFM × Δh
If Makeup Air comes from an air-conditioned department store hall:
BTU/h ≈ Area × 700–900 BTU/h·m²

For this example department store bathroom, it can be concluded that:
Exhaust Fan ≈ 1,200 CFM
Air Conditioning ≈ 4 TR
Supply Air ≈ 900 CFM
Transfer Air ≈ 300 CFM

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