Create your Air Handling Unit (AHU) 

Create your Air Handling Unit (AHU) scheme by using element palette and other tools (see help video). If there are no fatal errors, AHU will be calculated with a high probability (if “Calculation Countdown” > 0). If there are insufficient or wrong input data, error messages in the bottom of the page may help you. In this case you don’t have to pay (you’ll pay only if the calculation was successful). If you can’t solve the problem by yourself and you have an account, send message (calculation date, project name, AHU name, your question) to administrator. We’ll consider the problem, and you’ll get the answer.

Summer & winter

Summer & winter.  Air Handling Unit (AHU) element set for summer and winter are different. Anyway you have to make 2 calculations. But you have two options:

-        To create 2 separate schemes for winter and summer.

-        To create 1 general scheme, including all necessary elements for both sets. In that case extra elements for one of the calculations AHU calculator will ignore  & 

Input data

Input data. Pay attention to UNITS options (IP or SI) and select the required.

Minimal   INPUT DATA set is:

-        Outdoor air properties (temperature T and relative humidity rH);

-        Indoor air requirements (IAQ) (drybulb temperature T);

-        Air flow rate (“FAN” element).  result 


-        Recirculation flow rate or recirculation percentage.  result 

If your AHU has “RECUPERATOR”:

-        Recuperation heat rate.  result 

Optional INPUT DATA provides more complete result : result 

For “FAN” element -

-        Fan total pressure allows you to consider the fan power.

For “INDOOR” (IAQ) criteria. Handling the air means that the air will be delivered into the work spaces with IAQ (Indoor Air Quality) treatment. -

-        Relative humidity rH (or dew-point TDP or wet-bulb Tw or humidity ratio W). If there is indoor humidity requirement.

-        Heat load;

-        Wet load or latent heat load. In that case “Tornado”   determines the desired AHU discharge temperature and humidity to absorb energy and moisture from the room thermal load.


For elements using chilled or hot water for heat exchanging (“HEATING COIL”,”COOLING COIL”, “WASH COOLING”,” WASH HEATING”) –

-        Supply water temperature ( t1w );

-        Return water temperature ( t2w). It allows to get required water flow rate in the result.


-        Recirculation air properties (temperature and humidity ratio,

if it’s NOT equal to inside parameters) .  result 

Account owner 

Account owner has important advantages:

-        Cost savings.

-        Saving input data for recalculation or updating input data for future recalculations. Account owner has access to all previous calculations input data.

-        Account owner may communicate with an administrator for technical advice or support. 

Double click on your account name to access your profile, to change signature or to send e-mail


For previous calculations access :

-        Login

-        Select the required calculation and double click.



Psychrometric calculator is a free service

Psychrometric calculator is a free service. (not AHU calculator)

There may be slight inaccuracy in the test calculations because of results rounding. For example:


Input:   results:    
T=20°C rH=45% TDP=7.7°C  W=0.00653kg/kg Tw=12.9°C
T=20°C TDP=7.7°C rH=44.9%   W=0.00652kg/kg  Tw=12.9°C
T=20°C Tw=12.9°C rH=45.3% W=0.00658kg/kg TDP=7.9°C

In the first calculation wet-bulb temperature (Tw) exact value is 12.85°C, it shows 12.9°C. So in the 3rd calculation:  wet-bulb temperature  (Tw) =12.9°C value causes  the slight inaccuracy compared to 1st and 2nd calculations.