Unit 317 session 6 convector heaters & calculations.

​Calculating heat emitter size

Open Ended

What do you think we mean by the term Heat emitter?

A heat emitter is any device that releases thermal energy to warm a space, such as a room or building.

Open Ended

Research what BS EN 442 relates to!

​BS EN 442-1:2014
Radiators and convectors.
Technical specifications and requirements.

BS EN 442 is a European Standard that specifies the requirements and test methods for radiators and convectors used for space heating.


It covers aspects such as design characteristics, materials, markings, and performance requirements.

Open Ended

There are many types of heat emitters, how many do you know?

Poll

Have you heard of a 'Kick space heater'?

• Yes

• No

Multiple Choice

Where would a 'Kick space' convector heater usually be used?

• Kitchen

• Bathroom

• Commercial workshop

• Living room

A kick space heater is a compact electric or hydronic heater designed to fit into the recessed space beneath cabinets—typically in kitchens or bathrooms.

Poll

Have you heard of a 'Curtain heater'?

• Yes

• No

A curtain heater, more commonly referred to as an air curtain, is a device installed above a doorway that blows a controlled stream of air downward to create an invisible barrier between two spaces—typically indoors and outdoors.

Multiple Choice

What type of building would best suit a curtain fan convector heater? 

• Kitchen

• Bathroom

• Shop fronts/Commercial workshop

• Living room

Poll

Have you heard of a Low Surface Temperature (LST) Radiator?

• Yes

• No

Open Ended

Research!

What is a low surface temperature radiator and Where would they be required? 

A low surface temperature (LST) radiator is a specially designed radiator that limits its external surface temperature to 43°C or less, preventing burns from contact.

They are required in locations with vulnerable individuals, such as schools, nurseries, care homes, and hospitals,

​Calculating heat emitter size

​Calculating the size of the heat emitter is not just a case of performing the heat loss calculations and selecting a heat emitter size.

Adjustments have to made using correction factors.

Radiator catalogues list radiator outputs but these outputs were obtained in a controlled laboratory environment using tests laid down by various British Standards.

Whilst these tests give accurate outputs in laboratory conditions, the requirement for the designer is to adjust these figures based upon BS EN 442.

According to BS EN 442, all radiators

manufactured in the EU have to undergo specific tests based upon a flow temperature of 75°C and a return of 65°C in a test room with a temperature of 20°C.

In addition, the flow and return connections were at the same end.

This is known as top, bottom, same end, or TBSE.

​The pipe arrangements that are common are:

● top, bottom, same end or TBSE

● top, bottom, opposite end or TBOE

● bottom, bottom, opposite end or BBOE (the most common arrangement in domestic heating systems)

​Most domestic systems in the UK are designed with flow and return temperatures and pipework arrangements that are different from those that were used under the test conditions of BS EN 442.

This means that to obtain the correct output, correction factors have to be applied.

in other words we can not rely on just choosing a radiator size from an manufactures catalogue.

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​Panel radiators are the most common used in the UK today, there are many different makes and each make has multiple sizes available.

​The link below opens a radiator sizing chart, lets look through it together and discus how we would use this type of chart.



2014-04-09-Kudox-Steel-Panel-Radiators-Technical-Data.pdf

​As we see initially it looks complicated, however its actually quite easy to use with a little practice.

Across the top we have the radiator type, the names can vary between manufacturers but the type will be the same.

​So in Yellow we have the radiator length.
In green the radiator height, (600mm is standard).
and in blue the radiator type, single convector etc.

​So to use the chart if we select a 1000mm long radiator that is 600mm high and a T11 type, we follow the row and column until they meet and this will tell us the radiators heat output.
In this case 1026 watts or 1.026KW.

​But if we look carefully, at the bottom of the sheet it tells us these figures are only correct if the radiator is installed with a 'Delta T' ΔT of 50 and a water temp of 70⁰c, it is also standard that these figures are with the radiator pipework TBOE.

So what is the ​'Delta T' ΔT

​Delta T refers to the difference in average temperature between the water circulating throughout your central heating system and the room temperature.

For example, if the room temperature is 20C and the average water temperature inside the radiators is 70C, the Delta T value is calculated as 70C – 20C = 50C (delta T 50)

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​So what if our systems needs are different?

​What if our flow temperature is 65⁰c,our return is 55⁰c, and our room temperature is 18⁰c, what would the ΔT be?
Well 65 + 55 = 120 ÷ 2 = 60⁰c.

60 - 18 = 42 therefore our ΔT would be 42⁰c.

​So what if our systems needs are different?

​

If we look at the chart to the right we see the correction factors for different flow temperature values.
In our last session we calculated the heat loss for a room, the result was 941 watts.

So for a ΔT of 42 we would need to divide our heat loss of the room by 0.75 (The next value under 42)

941 ÷ 0.75 = 1,254.66 or 1255 watts.

​So what if our systems needs are different?

​ there is also a correction factor of 0.98 for pipework BBOE. therefore if our room has a heat loss of 1255 watts we divide by our correction factors to get our true heat loss value.

1255 ÷ 0.98 (for BBOE) = 1281 watts.

In other words because are flow and return temperatures are different to what the radiators have been tested on we need to fit a larger radiator than we first thought.

BBOE = ÷ 0.98

​So we see we need a radiator which give an output of 1372 watts to fully heat our room

​The picture shows a typical family home, use the information given to calculate the REAL heat loss values for each room and complete the following questions, your flow temperature is 55⁰c and return temperature is 45⁰c, the radiators are piped BBOE with a conversion factor of 0.98.

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So we can see using the correction factors for different flow and return temperature and different valve positions can make a big difference to the size of heat emitter needed in a room:

​Room	​Original heat loss	​New heat loss	​Difference
​Lounge	​2400	​5973	​3573
​Bed 1	​1400	​2801	​1401
​Bed 2	​1700	​3401	​1701
​Kitch	​860	​1721	​861
​Bath	​2400	​5973	​3573
​Cloak	​460	​920	​460
​Hall	​960	​1921	​961