Hello everyone and welcome to the new episode of the HVAC Education Hub Channel.
In this episode, we'll cover how to calculate heat loss with the differences between indoor and outdoor temperatures. We'll also compare different outdoor temperatures and their implications for heat loss calculations.
Heat loss is calculated based on the difference between indoor and outdoor temperatures. Different countries have varying standards and regulations for these calculations. For example, in the UK, regulations typically require that heat loss be calculated for 100% of the expected outdoor temperature range. But what does 100% mean? It means considering the average minimum temperature over a period, ensuring that heat loss is accounted for during the coldest expected conditions.
In some countries, you have the option to use different percentiles, such as 99.6% or 99%. Here’s an example for Zagreb, Croatia:
• For a 99.6% design, the minimum outdoor temperature is -9.3°C. This means that 0.4% of the year will be colder than this temperature.
• For a 99% design, the minimum outdoor temperature is -6.7°C. This means that 1% of the year will be colder than this temperature.
Using a statistical deviation allows us to balance the heat pump capacity with the actual needs throughout the year. Designing for 100% of the lowest temperature could result in an oversized unit for most of the year.
Let's consider Zagreb's historical temperature data:
• In the last 5 years, the minimum temperature was -15°C.
• In the last 10 years, it was -17°C.
• In the last 20 years, it was -19°C.
• In the last 50 years, it was -21°C.
Designing your heating system for the extreme low temperatures that occur only a few hours in 50 years doesn't make practical sense. Instead, using a 99% or 99.6% design temperature is more reasonable.
Let’s see an example:
• If the design outdoor temperature is -12.6°C and the indoor temperature is 20°C, the temperature difference is 32.6°C. If the heat loss for a house is 9.78 kW at this temperature difference, then the heat loss per degree Celsius is:
9780 / 32.6 °C = 300 W/°C
• At an outdoor temperature of -9.3°C, the temperature difference is 29.3°C. The heat loss would then be:
300 W/°C × 29.3 °C = 8.79 kW
• At an outdoor temperature of -6.7°C, the temperature difference is 26.7°C. The heat loss would then be:
300 W/°C × 26.7 °C = 8.01 kW
As you can see, there is a significant difference in heat loss between -6.7°C and -12.6°C, highlighting the importance of choosing the correct design temperature.
Choosing the appropriate design temperature affects the capacity of your heating system and ensures efficiency. Oversizing the system can lead to inefficiencies and increased costs. Each country may have different recommendations, and you can find detailed information for different cities on websites like ASHRAE.
Thank you for watching. Subscribe to my channel and follow me on LinkedIn. Feel free to send me an email or message with feedback or questions so we can continue learning about heating systems together.
ASHRAE link:
ashrae-meteo.info/v2.0/index.php
Check the HVAC analysis on my LinkedIn profile:
/ mario-dodic
E-mail for collaboration or requests:
📩 hvaceducationhub@gmail.com
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