CIBSE cooling loads conduction gain
CIBSE cooling loads conduction gain
I have a simple house project, in which i'm only interested in one room, with quite large windows, largely south facing. i keep this room at 24degC max all year, 28degc outside max. .Peak summertime cooling (in august) includes conduction gain which is negative to the tune of -2kW max, so basically a heat loss. How can this happen when outside is warmer that 24? furthermore the peak day graph shows actually negative conduction values start pretty much when the sun is up in the morning. any ideas please?
Re: CIBSE cooling loads conduction gain
HI Akraw,
When looking at internal and external conduction, the software sees the boundary of a room as being the internal surfaces of its external walls and internal surfaces of its internal walls. Any heat which passes this boundary is reported as internal or external conduction depending on whether the wall is internal or external.
This means that conduction as reported in Vistapro actually represents the amount of heat that is transferred from the air in the room to the thermal mass of the walls or vice versa. Negative conduction gains means heat is being absorbed by the walls - the internal conduction gain represents heat being absorbed or released by the internal walls. With an ApacheSim, you could view a breakdown of the conduction gains (output options) to see where the main heat transfer is occurring however this is not possible with CIBSE Loads. You could however check the constructions assigned to the room – if these appear to have thermal mass then it would affect your internal conduction gains.
The conduction calculations are based on the CIBSE Admittance method.
When looking at internal and external conduction, the software sees the boundary of a room as being the internal surfaces of its external walls and internal surfaces of its internal walls. Any heat which passes this boundary is reported as internal or external conduction depending on whether the wall is internal or external.
This means that conduction as reported in Vistapro actually represents the amount of heat that is transferred from the air in the room to the thermal mass of the walls or vice versa. Negative conduction gains means heat is being absorbed by the walls - the internal conduction gain represents heat being absorbed or released by the internal walls. With an ApacheSim, you could view a breakdown of the conduction gains (output options) to see where the main heat transfer is occurring however this is not possible with CIBSE Loads. You could however check the constructions assigned to the room – if these appear to have thermal mass then it would affect your internal conduction gains.
The conduction calculations are based on the CIBSE Admittance method.
Re: CIBSE cooling loads conduction gain
hi terence
thank you for your quick reply.
i have also re-ran this in apache, and also got negative conduction gains for most of the summer day. my walls are lightweight,i re-ran it with heavyweight wall and results are worse (i.e more negative gains).
The conduction gain contributes to cooling load but since it's negative ,it reduces it which doesn't seem reasonable. do you know the solution to this? many thanks in advance
thank you for your quick reply.
i have also re-ran this in apache, and also got negative conduction gains for most of the summer day. my walls are lightweight,i re-ran it with heavyweight wall and results are worse (i.e more negative gains).
The conduction gain contributes to cooling load but since it's negative ,it reduces it which doesn't seem reasonable. do you know the solution to this? many thanks in advance
Re: CIBSE cooling loads conduction gain
If you plot solar gain on the graph you should see that conduction gain is the inverse of solar gain.
As the solar radiation passes into the space, a quantity is absorbed by the building fabric, hence a negative conduction gain as the heat is passing from the space and into the fabric/ thermal mass.
As the space cools the heat is released from the thermal mass back into the space therefore you get a more positive conduction gain.
As the solar radiation passes into the space, a quantity is absorbed by the building fabric, hence a negative conduction gain as the heat is passing from the space and into the fabric/ thermal mass.
As the space cools the heat is released from the thermal mass back into the space therefore you get a more positive conduction gain.