Explanation of indoor surface temperature calculation (condensation check) [Equipment calculation sheet that can be understood in 3 minutes]

質問・疑問

There is a risk of condensation…
How do I calculate the surface temperature of the floor and walls?
Please tell me a simple way to calculate the indoor surface temperature!

This time, we will answer these questions.

In “Equipment Calculation Sheets in 3 Minutes,” we provide a simple explanation of calculation methods for building equipment that can be understood in 3 minutes.

For more detailed explanations, please refer to the recommended equipment books .

This article explains how to calculate indoor surface temperatures.

What is indoor surface temperature calculation?

Indoor surface temperature calculations are performed to check whether there is a risk of condensation or whether there is a need to increase insulation performance.

The following article explains that the heat added to a room is generated by the temperature difference between the inside and outside of a building, separated by structural elements such as the walls, floors, ceilings, and roofs.

Explanation of the calculation method for passing heat load (structural load) in heat load calculation

The surface temperature of the walls, floors, ceilings, etc. inside the room changes depending on the temperature difference between inside and outside.
Depending on the indoor surface temperature, condensation may occur or the air conditioning may become less effective.
Therefore, in addition to sufficient air conditioning equipment, architectural insulation is also necessary.

How to calculate indoor surface temperature

The indoor surface temperature can be calculated using the ratio of temperature difference and thermal resistance.
The calculation formula is as follows.

calculation formula

( ti – ts ) / ( ti – to ) = Ri / R
↓
ts = ti – ( ti – to ) × Ri / R 

Formula legend

ts: Indoor surface temperature [℃]
ti: Indoor temperature [℃]
to: Outside temperature [℃]
Ri: Indoor heat transfer resistance [m2・k/w]
R: Floor thermal resistance [w/m2・k]

Calculation example

This is an example of a calculation to verify whether the insulation performance is sufficient, assuming a situation in which condensation may occur due to the cold floor on the bottom floor in summer.

Conditions
Indoor temperature: 26°C Indoor humidity: 40%　
Indoor dew point temperature: 11°C (from indoor temperature and humidity)　
Underground temperature: 5°C　
Indoor heat transfer resistance: 0.11m2・k/w Floor heat transfer resistance: 0.28w/m

Calculation result:
ts = 26 – (26 – 5) × 0.11 / 0.28 = 17.6℃
17.6℃ > 11℃ OK
∴Since it is unlikely that the indoor surface temperature will fall below the indoor dew point temperature, there is no problem with insulation performance.

summary

This article explains how to calculate indoor surface temperatures.

We will not go into detail in this article, but it can be calculated from the temperature difference and thermal resistance ratio of the target parts, so it is possible to calculate the surface temperature of an exterior wall, for example.

This article simply summarizes the calculation method.
For more detailed information, please see the following book.
If you don’t have it, I recommend purchasing it.

空気調和設備計画設計の実務の知識

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空気調和・衛生設備の知識

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I hope this article will be helpful to you in your work and qualification studies.

» Reference: Tips and study methods for passing the building equipment engineer exam [Pass the theory by self-study, and the drafting by attending a course]

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» Reference: Explaining how to study to pass the final examination for the first-class architect facility design exam [Get past exam questions]

This concludes our explanation of indoor surface temperature calculations (condensation checks) [Equipment calculation sheet you can understand in 3 minutes].