ktgottfr
Mechanical
- Apr 14, 2008
- 46
Greetings all,
I have been working on an HVAC calculation for a shelter made from a standard sea container. I have been using ASHRAE 2001 as a guide. However, I was asked by the clients to take a 50km/hr wind into account in the heat loss and/or gain through the walls.
My problem is that ASHRAE Fundamentals 2001 does not seem to mention any effect due to wind speed in any of its simplified methods. It seems to say that heat loss through the walls is treated as conduction only.
What I initially did, was use the Canadian Windchill Index to find the apparent outdoor temperature at a 50km/hr wind, and used this as my outdoor air temperature in the calculations. I thought that this would probably be a conservative estimate.
But, if I use the windchill index for cold ambient temperatures, what should I be using for warm ambient temperatures? I had assumed that even when the outside temperature is warmer than the shelter interior temperature, the effect of the wind would be to cool the shelter, and therefore I ignored wind effects for the shelter cooling load. But a colleague here has taken issue with this assumption, suggesting that increased windspeed would increase the convective heat transfer rate, and therefore actually heat the shelter if the outdoor temp is higher than the interior temp.
What I finally decided, was that since the heat transfer through the walls is purely due to conduction, then the convective heat transfer should have no effect. Therefore, it was incorrect of me to add a windchill effect (or a windheating effect). The only place where the increased wind will have an effect with the simplified methods would be on air infiltration.
Does this sound right to anyone? I had initially posted in the HVAC forum, but this forum seems more appropriate, since my question is directly about ASHRAE. Thanks everybody!
-Kristjan
I have been working on an HVAC calculation for a shelter made from a standard sea container. I have been using ASHRAE 2001 as a guide. However, I was asked by the clients to take a 50km/hr wind into account in the heat loss and/or gain through the walls.
My problem is that ASHRAE Fundamentals 2001 does not seem to mention any effect due to wind speed in any of its simplified methods. It seems to say that heat loss through the walls is treated as conduction only.
What I initially did, was use the Canadian Windchill Index to find the apparent outdoor temperature at a 50km/hr wind, and used this as my outdoor air temperature in the calculations. I thought that this would probably be a conservative estimate.
But, if I use the windchill index for cold ambient temperatures, what should I be using for warm ambient temperatures? I had assumed that even when the outside temperature is warmer than the shelter interior temperature, the effect of the wind would be to cool the shelter, and therefore I ignored wind effects for the shelter cooling load. But a colleague here has taken issue with this assumption, suggesting that increased windspeed would increase the convective heat transfer rate, and therefore actually heat the shelter if the outdoor temp is higher than the interior temp.
What I finally decided, was that since the heat transfer through the walls is purely due to conduction, then the convective heat transfer should have no effect. Therefore, it was incorrect of me to add a windchill effect (or a windheating effect). The only place where the increased wind will have an effect with the simplified methods would be on air infiltration.
Does this sound right to anyone? I had initially posted in the HVAC forum, but this forum seems more appropriate, since my question is directly about ASHRAE. Thanks everybody!
-Kristjan
