Tom Posted December 10, 2008 Report Share Posted December 10, 2008 Just curious, Thinking about the purchase of an Arctic tub with its great insulation but a friend brought up the subject that if the cabinet is so well insulated for the winter what happens in the summer months, does the cabinet overheat. Thank you for your interest in Arctic Spas. Our product was engineered for the Canadian winter, and it's ironic that we sometimes have to undo all that wonderful energy efficiency. An automatic thermal cutoff prevents the motors from overheating. For those of you fortunate enough to live in warmer climates, we offer screened louvered doors or the active cooling of the Arctic Chiller (I apologize that neither of those products appears on our web site). Quote Link to comment Share on other sites More sharing options...
Tom Posted December 10, 2008 Report Share Posted December 10, 2008 But first a complete seal and R-15 to R-20 on the side walls will need to be established. I made up the following scenario to practice calculating R value, this is assuming constant outside temp and power off, constant pressure, constant volume, and a monotomic gas to keep things simple. I think that I did something wrong, my answer seems low. Outside Temp = 30 F Inside Initial Temp = 90 F Inside Final Temp = 60 F Time period = 1 hr 4 side walls at 3' X 8' Estimated air volume = 70 ft^3 = 1982179 cc material thickness = 0.75" Convert from F to K, subtract Temp final K from Temp initial K (16.5) multiply delta T (in K) by 0.001297 J/cm^3 * K(specific heat of air at sea level) and 1982179 cc to get joules of energy transfer required to decrease the temperature of the body of air inside the cabinet divide by 3600 seconds to get watts (550) divide watts by [area (10.7) X temperature differential (33)] multiply this answer by material thickness (0.01905) in meters to get thermal conductivity of the walls (0.0297 W/M*K) Divide material thickness by thermal conductivity to get R value of 0.64 Does that sound right? Thanks, -J Thermal conductivity is substance specific, and you haven't said what the substance is. You've worked backwards from a formula for heat loss through a wall and as far as I've checked it, your work looks okay except that you haven't accounted for heat loss through top or bottom. That R value is about right for 3/4" of some materials but you can look that up in readily available tables without all that work. Quote Link to comment Share on other sites More sharing options...
1bad88 Posted December 10, 2008 Author Report Share Posted December 10, 2008 Thermal conductivity is substance specific, and you haven't said what the substance is. You've worked backwards from a formula for heat loss through a wall and as far as I've checked it, your work looks okay except that you haven't accounted for heat loss through top or bottom. That R value is about right for 3/4" of some materials but you can look that up in readily available tables without all that work. Tom, Thank you for the response. I tried to start with a vary basic problem and I was basing all of my calculations strictly on energy transfer through a simple surface area. I did say wall, but the example is just total surface area through which the energy is transferred, and it all assumes that all the transfer is even. I haven't ever taken a Thermodynamics course, so there's a lot I don't know. The numbers that I used were contrived, so if the resulting thermal conductivity (0.0297 W/M*K) happens to match any material it was pure dumb luck. Best Regards, -J Quote Link to comment Share on other sites More sharing options...
elbrecht Posted December 17, 2008 Report Share Posted December 17, 2008 Well, my lights went out last week so I got to check theory against reality. Lights went out on Dec 11, at 10PM. Outdoor temp was hovering around freezing for 24 hours. Cabinet temperature dropped about 10 degrees overnight. The next 24 hours the temp ranged from 15-30. The next day stayed around 20-25 degrees F. By Sunday 830AM, the power had been out almost 60 hours & the outdoor temp had stayed below freezing. The cabinet temp was 62.5F. [this is when I started paying closer attention as I had the rest of the house pretty well buttoned down] 4PM, outside 33F, cabinet 62.1 8PM, outside 25F, cabinet 60.8 12PM, outside 30, cabinet 59.9 Monday 7AM, outside 35F, cabinet 58.5 9AM, outside 43F, cabinet 58.3 1PM, outside 53F, cabinet 59.8 3PM, outside 54F, cabinet 59.9 [note the solar gain on the last 2<g>] It was so warm and I expected the outage to go 2 more days so I popped the cover, tested the water [FC of 1ppm] and added chlorine in a bucket of hot water- partly to dilute it some and partly to replace the BTUs lost by the cover getting opened. 8PM, outside 53F, cabinet 59.9 Then the lights came on at 9PM so the ‘experiment’ ended. I now have a generator so if this happens again & the weather is harsher I’ll drop a stock tank heater in for a couple hours to take the chill off. But even if it is 20-30 degrees below freezing I won’t be too worried for a couple days. Jim Quote Link to comment Share on other sites More sharing options...
tpyke Posted June 24, 2009 Report Share Posted June 24, 2009 Where would be the best temperature probe placement to accurately monitor the cabinet temp? I noticed that if I place it near the motor it will get very hot as compared to when I place it on the door. Quote Link to comment Share on other sites More sharing options...
1bad88 Posted June 24, 2009 Author Report Share Posted June 24, 2009 You might want to be careful about how you ask such questions, some people around here are unfriendly to this topic What are you trying to accomplish by tracking your cabinet temperature? Are you trying to make sure that your motors don't overheat, prevent freezing, or are you thinking about measuring energy loss (too many variables to track with any sort of accuracy)? -J Quote Link to comment Share on other sites More sharing options...
tpyke Posted June 24, 2009 Report Share Posted June 24, 2009 You might want to be careful about how you ask such questions, some people around here are unfriendly to this topic What are you trying to accomplish by tracking your cabinet temperature? Are you trying to make sure that your motors don't overheat, prevent freezing, or are you thinking about measuring energy loss (too many variables to track with any sort of accuracy)? -J Overheating. I just insulated my spa and am wondering if I need to ventilate the cabinet at all during the summer months and if so how much. I just replaced every electrical component on this spa except for the motor, so I would like to try to extend its life as much as possible to not have to buy one of those too...it's already 15 years old! On the motor itself it is written "ambient 40C" . Would that be the max temperature or the recommended? Quote Link to comment Share on other sites More sharing options...
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