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***** Prologue 4/29/11 4:40 Eastern time ********
To those reading this thread:
I've presented a number of questions, only one of which had to do with getting educated ~rough~ estimates of how many tons of cooling capacity I might need. Some people were willing to give one, others were adamant about not doing so. To those who might be willing to offer one, I'd like to provide some additional information. I do this in large part because I have yet to find any software that is geared toward steel buildings.
My three 1,000 sq. ft. units are in the middle of a single steel building that contains 10 virtually identical units. The 3 units are all open to one another. The back walls are to the south and have no windows. The front walls are to the north and have 3 12 x 12 insulated overhead doors (R - 16.04) with a total of 24 sq ft of insulated (double-pane) lites in them. There are also 3 steel entry doors on the north side. One side wall of the 3,000 sq foot total area abuts an unheated unit, and the other side wall abuts a heated unit. Air infiltration is minimal. Lighting consists of sixty 8' 95W HO T-12 fluorescent tubes powered by 30 electronic ballasts.
If you are inclined to offer a rough estimate, great. If not, please don't tell me to "do a load calc", because one or more will be professionally done prior to purchasing any equipment. I am interested only in getting rough estimates from those who are willing to provide one.
Lastly and most importantly:
The sizing issue is really secondary to what has evolved into my main question: how do you guys approach the apparent trade-off between having enough cooling capacity to achieve a target indoor temperature on the hottest day of the year, and not having so much capacity that the compressor(s) short-cycle(s) during the less demanding part of the cooling season, thereby reducing system efficiency and negatively affecting dehumidification?
I've personally experienced the opposite situation; a residential split system that could not keep the indoor temperature below 80 on the hottest days of the year (around 100 F.), and had to be supplemented by a window unit. It was a 2-ton system, and probably should have been 2.5 tons.
But even if it had been sized more properly, it still seems to me that there's a trade-off between cooling capacity and cycle times. Is it simply undesirable and/or impossible to have a system that will keep a given space at a certain target temperature on the hottest day of the year, and still offer acceptable SEER and dehumidification during the rest of the cooling season? If it is a trade-off, which way do you go? Do you tend to tell your customer that if they're willing to be a little warm on a few days, that they'll save money and have better dehumidification the rest of the season? If you had a customer who insisted on having enough cooling capacity to handle the hottest days, would you try to talk them out of it?
Also:
In this thread, I've tried, with limited success, to put forth a hypothetical situation in which it has been competently determined that my cooling load calls for exactly 5 tons. I'm on a limited budget (like most of the rest of the world), and will be using a used packaged roof unit or units. I would like to get some opinions on whether or not I would be better off, under this hypothetical situation, to go with a single 5-ton unit, or a combination of smaller units that could be controlled in such a way as to allow for greater flexibility for achieving a better compromise between raw cooling power and cycle times/SEER/dehumidification during periods of varying outside temperature. So I pose the hypothetical to try to achieve a real-life result; namely, not sweating in my shop this summer. I've received some very helpful answers involving two-stage and variable-output systems, but as a practical matter I'm probably going to be limited to plain old one-stage packaged units, so any input on how to divide the load between multiple units, or to not try to divide it at all, would be greatly appreciated.
Thanks.
***** Original thread follows.
OK, it's finally warming up in CT and I don't want to sweat through another summer. I'd appreciate some advice on what brands and sizes of rooftop units and air handlers to get.
I have three adjacent 1,000 sq ft units in a Butler steel building. Average ceiling height is 13.5 ft for a total of 40,500 cubic feet. Insulation is minimal; R-11 in ceiling and walls, three insulated 12' X 12' doors on north side, no windows on south side, concrete slab floor. No major heat sources to speak of; refrigerator, 30 HP air compressor that will probably run 1% of the time, computer, metalworking and woodworking machines that will run no more than 2 at a time, and nowhere near continuously; two people on average, 1 dog, 1 cat. (Dog has been instructed to pant outside).
So, a series of questions:
1) How many tons do I need? I know I don't want to over-size, but I want to be moderately comfortable on 100-degree days. The concrete slab helps a little, but with no A/C, if it's 100 outside it's probably 90 inside. Can I have a system that will keep it at 70 inside when it's 100 outside, and not be too big?
2) Should I get one system and duct it to the two adjacent 1,000 sq ft shops, or am I somehow better off with separate systems?
3) Should I get a "packaged" system (compressor, condenser, air handling all-in-one), or separate compressor(s) and air handler(s).
4) What specific brands/models are good?
5) I'm going to be buying used if possible. What kinds of prices would be fair? What should I look out for to avoid getting junk?
6) What am I leaving out?
Thanks in advance.
To those reading this thread:
I've presented a number of questions, only one of which had to do with getting educated ~rough~ estimates of how many tons of cooling capacity I might need. Some people were willing to give one, others were adamant about not doing so. To those who might be willing to offer one, I'd like to provide some additional information. I do this in large part because I have yet to find any software that is geared toward steel buildings.
My three 1,000 sq. ft. units are in the middle of a single steel building that contains 10 virtually identical units. The 3 units are all open to one another. The back walls are to the south and have no windows. The front walls are to the north and have 3 12 x 12 insulated overhead doors (R - 16.04) with a total of 24 sq ft of insulated (double-pane) lites in them. There are also 3 steel entry doors on the north side. One side wall of the 3,000 sq foot total area abuts an unheated unit, and the other side wall abuts a heated unit. Air infiltration is minimal. Lighting consists of sixty 8' 95W HO T-12 fluorescent tubes powered by 30 electronic ballasts.
If you are inclined to offer a rough estimate, great. If not, please don't tell me to "do a load calc", because one or more will be professionally done prior to purchasing any equipment. I am interested only in getting rough estimates from those who are willing to provide one.
Lastly and most importantly:
The sizing issue is really secondary to what has evolved into my main question: how do you guys approach the apparent trade-off between having enough cooling capacity to achieve a target indoor temperature on the hottest day of the year, and not having so much capacity that the compressor(s) short-cycle(s) during the less demanding part of the cooling season, thereby reducing system efficiency and negatively affecting dehumidification?
I've personally experienced the opposite situation; a residential split system that could not keep the indoor temperature below 80 on the hottest days of the year (around 100 F.), and had to be supplemented by a window unit. It was a 2-ton system, and probably should have been 2.5 tons.
But even if it had been sized more properly, it still seems to me that there's a trade-off between cooling capacity and cycle times. Is it simply undesirable and/or impossible to have a system that will keep a given space at a certain target temperature on the hottest day of the year, and still offer acceptable SEER and dehumidification during the rest of the cooling season? If it is a trade-off, which way do you go? Do you tend to tell your customer that if they're willing to be a little warm on a few days, that they'll save money and have better dehumidification the rest of the season? If you had a customer who insisted on having enough cooling capacity to handle the hottest days, would you try to talk them out of it?
Also:
In this thread, I've tried, with limited success, to put forth a hypothetical situation in which it has been competently determined that my cooling load calls for exactly 5 tons. I'm on a limited budget (like most of the rest of the world), and will be using a used packaged roof unit or units. I would like to get some opinions on whether or not I would be better off, under this hypothetical situation, to go with a single 5-ton unit, or a combination of smaller units that could be controlled in such a way as to allow for greater flexibility for achieving a better compromise between raw cooling power and cycle times/SEER/dehumidification during periods of varying outside temperature. So I pose the hypothetical to try to achieve a real-life result; namely, not sweating in my shop this summer. I've received some very helpful answers involving two-stage and variable-output systems, but as a practical matter I'm probably going to be limited to plain old one-stage packaged units, so any input on how to divide the load between multiple units, or to not try to divide it at all, would be greatly appreciated.
Thanks.
***** Original thread follows.
OK, it's finally warming up in CT and I don't want to sweat through another summer. I'd appreciate some advice on what brands and sizes of rooftop units and air handlers to get.
I have three adjacent 1,000 sq ft units in a Butler steel building. Average ceiling height is 13.5 ft for a total of 40,500 cubic feet. Insulation is minimal; R-11 in ceiling and walls, three insulated 12' X 12' doors on north side, no windows on south side, concrete slab floor. No major heat sources to speak of; refrigerator, 30 HP air compressor that will probably run 1% of the time, computer, metalworking and woodworking machines that will run no more than 2 at a time, and nowhere near continuously; two people on average, 1 dog, 1 cat. (Dog has been instructed to pant outside).
So, a series of questions:
1) How many tons do I need? I know I don't want to over-size, but I want to be moderately comfortable on 100-degree days. The concrete slab helps a little, but with no A/C, if it's 100 outside it's probably 90 inside. Can I have a system that will keep it at 70 inside when it's 100 outside, and not be too big?
2) Should I get one system and duct it to the two adjacent 1,000 sq ft shops, or am I somehow better off with separate systems?
3) Should I get a "packaged" system (compressor, condenser, air handling all-in-one), or separate compressor(s) and air handler(s).
4) What specific brands/models are good?
5) I'm going to be buying used if possible. What kinds of prices would be fair? What should I look out for to avoid getting junk?
6) What am I leaving out?
Thanks in advance.
