What is U value? And how to find the U values?

U value in HVAC is the amount of heat transferred per meter per degree by the material

More U more heat transfer. The reciprocal of U is R (resistance) so more R less heat transfer

 

There are certain U values for certain material which you will find in ASHRAE fundamentals as property of materials.

The overall U value is taken when the wall has many components like there will be a plaster or cladding so all the values are sum up as R not U and then overall U value is calculated,.

 

Hope this will work

U value is Overall heat transfer coefficient or the rate at which Heat transmits through a building component such as Wall, Roof etc. If U value is low then heat tranmittance is also less. U-value is the inverse of R-value.R-Value known as Thermal resistance is the ability of a material to prevent the tranfer of heat.The U-value of a construction component of several layers can be calculated using formula as below:U =1 / R1 + R2 + R3 or ∑ R. U value is used to calculate heat transmission through a building element with formula Ht = U A dt. Ht = heat flow (Btu/hr). U = overall heat transfer coefficient, (Btu/hr ft2 F). A = wall area (ft2). dt = temperature difference (F).

u value is the measure of heat transfer coefficient which is employed in building services when assigning heat load calculation for the building .which is equal sum of the total materials used up ,generally in uae we employ hollow blocks with insulation board on between to reduce u value.

U value is the measure of overall value of a building insulation to heat transfer. It could collected depending on addition of all the architectural resistances of the member components. It could be calculated by finding the reciprocal of the sum of all materials making the building member.

In cooling load estimation, U factor is used as a heat transfer coefficient applicable to partition walls, external walls, glass wall, glass windows, skylights materials etc.

U factor specifies the heat transfer factor of the materials used in fabrication of the above partitions, and glasses.

Standard values as a thumb rule to be followed for this U factor.

 

Please refer Ashrae for the different U values of different materials.

U-value is more of an engineering term which describes thermal performance. It has traditionally been applied to materials such as window ,wall, floor or roof 

U-Value (of building element) = 1 / (Rso + Rsi + R1 + R2 …)

Rso  is  fixed external resistance

Rsi is the fixed internal resistance

R1 & R2  is resistivity of all elements