newdeal
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| 09/22/2009 6:43 PM |
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| Ok so we have gotten 4 estimates for geo in our home and all 4 are differant. We have a 1900 square foot bungalo in Niagara Falls Ontario Canada and our heat loss was estimated 41000 through an energy audit and 47000 by one of the geo guys... The 4 bids are as follows
1) 5 ton unit, with either 3000 or 3600 feet of 3/4" buried pipe depending on if we want extra buried 4 feet below the ground pipes 2 feet apart (this guy does Geosmart units)
2) 4 ton unit with 2000 feet of 1 1/2" buried pipe at 5 feet deep pipes 20" apart (this guy does waterfurnace units)
3) 4 ton unit with 3000 feet of 3/4" buried pipe at 5 feet deep, pipes 20" foot apart (this guy does Nordic units)
4) 3 ton unit with 1800 feet of 3/4" buried pipe at 5 feet deep pipes 2 feet apart (this guy does next energy units, same as climatemaster)
The only one who did any calculations was the last guy and he said the auxillary heat will run 2% of the time based on our damp clay soil type and so going with a 4 ton unit will be draftier, noisier and only save about $6 per year since the 3 ton will create more hot water so will nearly compensate for the cost of the auxillary heat. He also had the engineer come out (Next energy aka climatemaster in the states) and even showed us some tables that indicated the unit run time depending on the temperature outside and when the crossover is to electric etc (according to this the second stage will come on around 32 fahrenheit or 0 celcius and the aux heat will kick in when it gets around 17 fahrenheit which is about -8 celcius I think). I am inclined to go with him since its cheaper for one and for two he explained everything and actually did a heat loss calculation etc but its hard when you have so many conflicting estimates as to know which to go with an you don't want to undersize your system and currently we have an old 80,000btu electric furnace that only keeps one half of the house warm (which is apparently due to ducting issues) and runs almost all the time. Anyway I was hoping for someone elses opinion as to which system sounds like it will best meet our needs. The aux heat on the 3 ton unit says it will come on at 17 fahrenheit and on the 4 ton unit at 2 fahrenheit, I am torn because the 3 ton seems so borderline that if it doesnt work as well as expected then we might be in a bit of trouble and it says it will operate like 3800hours a year (almost 50% of the time) which seems like alot! |
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dkubarek
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| 09/22/2009 7:20 PM |
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| I'm a noob but your piping sounds way off. You usually use about 150-200 feet of piping per ton. Double check that. I would go with the estimate from the guy who actually did a manual J calculation or ask the others to do the same. 3 ton sounds decent if your home is well insulated. (my manual Js suggested 3 ton on a 2,000 sq. ft. new construction. But maybe 4 tons is needed if you have poor ins.) I also think you can adjust when the aux. unit comes on or disable it entirely using some thermostats or unplugging the unit. But others here will know better. |
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newdeal
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| 09/22/2009 7:39 PM |
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| its an 1800-1900 sqft bungalo with finished basement. Definately everyone has said 600 feet of pipe per ton. Some guys did an extra 600 to be safe. We get alot of wind in the winter as we are in the middle of a big field. I am not sure that the calculations that the guy did took that into account. Our house they esitmate asd R20 in the walls and R44 in the cieling with an air inflitration of around 1100cm^2 from the door blower test |
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engineer
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| 09/22/2009 8:26 PM |
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150-200 feet per ton applies to vertical loops in many areas (alas, not Florida)
600 feet/ton sounds reasonable for trenched horizontal systems, but it is better to have a bit too much pipe in the ground than too little.
I'm with what Joe A suggested at Geoexchange - 3 tons sounds optimal - occasional use of strips will be offset by lower installed cost. 3 tons will be more comfortable in summer as well - better dehumidification.
OK for unit to run many many hours - result is comfortable, quiet, efficient, even heat, though I will say that 3800 hours per year seems a tad high - mine logged 2000 hours in the first full year, but it is a bit oversized and located in Florida. |
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Without data, you only have an opinion. |
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newdeal
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| 09/22/2009 9:07 PM |
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| i was wrong its 3800 hours for heating and 770 for cooling so more like 4400-4500 hours per year running |
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engineer
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| 09/22/2009 9:19 PM |
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Hmm. I will defer to the northern professionals, but that seems high. It implies near continuous operation for several months per year, and I think that means the unit would be quite undersized.
My experience suggests that a unit should run 12 or so hours on a cooling 'design day'. A 'design day' is a day of weather near but not at the extreme for a particular climate. In cooling that would entail near continuous operation from 1-2 PM through sundown, and intermittent operation outside those hours. In heating it would be the inverse - and probably a bit longer, perhaps 16-20 hours during a design day with aux coming on for several late night / early morning hours. But most days are milder than design days, and I'm having trouble making those numbers add up to so many hours.
Again - best wait for a northern pro or two to comment. |
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Without data, you only have an opinion. |
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joe.ami
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| 09/22/2009 9:49 PM |
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Based on the info you provided the 3 ton is a good fit. I notice the bin analysis indicates your area is a little warmer than mine (Lansing MI) though you are north of me. This strikes me as odd....some sort of lake effect?
If your numbers are good, I trust my software.
Good Luck,
Joe
(I thought I recognized the question, but didn't see my reply...... I moved it from the other site.....j). |
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TechGromit
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| 09/23/2009 7:38 AM |
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Posted By newdeal on 09/22/2009 6:43 PM
... we have an old 80,000btu electric furnace that only keeps one half of the house warm (which is apparently due to ducting issues) and runs almost all the time.
Are any of the contractors going at address your ducting issues? If the electric furnace can't keep the house warm, I fail to see how a different unit reguardless of heating type or btu output if going to solve this issue.
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joe.ami
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| 09/23/2009 7:55 AM |
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Posted By newdeal on 09/22/2009 6:43 PM
Ok so we have gotten 4 estimates for geo in our home and all 4 are differant. We have a 1900 square foot bungalo in Niagara Falls Ontario Canada and our heat loss was estimated 41000 through an energy audit and 47000 by one of the geo guys...The aux heat on the 3 ton unit says it will come on at 17 fahrenheit and on the 4 ton unit at 2 fahrenheit, I am torn because the 3 ton seems so borderline that if it doesnt work as well as expected then we might be in a bit of trouble and it says it will operate like 3800hours a year (almost 50% of the time) which seems like alot!
A 41,000 BTU load served by a 3 ton geo can hardly be called borderline. You simply have bids from many 100% loaders who will cost you more through there ignorance.
If unit were undersized it would be running 7,600 hours a year (all the time).
TG brought up a good point;
Has anyone suggested duct modifications or said your duct work is poor?
Joe |
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newdeal
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| 09/23/2009 8:15 AM |
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| ok more info I called the guy who did my energy audit...the 41000btu is purely a guess he did no measurements to do this calculation whatsoever. The 47334btu did have calculations so I would be closer to that I will assume. Most guys said that my return ducting needs to be enlarged because it is not big enough. THe guy who said the 3 ton was better was basing it on the fact that he thought my airflow would be too high on a 4 ton unit for the ducting and therefore we may feel drafty or it may be loud. There are 18 vents in my house, each supplied by a 5" duct. The ducts coming off the furnace are an 18x8 for return, a 16x8 to supply the half of the house that always feels cold (7 ducts come off this main duct) and a 20x10 to supply the half of the house that feels warm (11 ducts come off this main duct). The cold duct feels cold even right by the furnace and the warm duct feels hot right by the furnace...there is no damper in the main duct but the plenum is a bit short because the cold duct comes off a bit lower since it travels underneath an area of out sunken living room. and then the hot duct bends off a bit higher up, they think that part of the issue may also be due to the airconditioner coil (which is not in use) blocking some of the airflow to the lower duct |
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joe.ami
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| 09/23/2009 8:24 AM |
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Again the 3 ton guys numbers work for me. He has put thought into your duct system and is the only one who actually did a heat loss.
Incidentally 47000 BTU's was what I put into my design software for you. Since you had listed 2 loads, I put in the largest before I endorsed his pick.
Joe |
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newdeal
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| 09/23/2009 8:26 AM |
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| we also have 4 returns which appear to be 14x6, none in the basement and none in the cold half of the house. The basement is mostly finished so access to some ducts is tough but the unfinished part of the basement is under the cold part of the house. When the main duct on the cold side of the house ends two 5" ducts come off the end of it, the guy also said that was bad they should come off the side of the duct not the end. All the ducts are metal ducts |
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newdeal
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| 09/23/2009 8:30 AM |
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| I am mostly concerned because with his numbers the crossover to aux heat is 17 fahrenheit and it gets cold here in canada and my house is in the middle of a field so it also gets windy and I am not sure if wind has been taken into account or not. I would hate to have not enough heat. Also the internal gains he used seem to be too high for use (8100btu) because we only have two people living here and the two of use dont use that much power so it seems like 6300btu is more accurate (I downloaded the geodesigner and started putting in numbers to test the differances). |
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newdeal
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| 09/23/2009 8:30 AM |
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| he also used a delta t of 69 degrees in his heat loss calc I am not sure if that is standard or not, the default on geodesigner is 65 |
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newdeal
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| 09/23/2009 8:32 AM |
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| sorry for all the posts but I was also wondering if we installed an extra loop in the 3 ton system (2400feet instead of 1800feet) it seems to make the system more efficient is there any issue with doing this such as then needing a higher flow to achieve turbulent flow or is it ok to add another loop without changing anything else? |
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engineer
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| 09/23/2009 9:16 PM |
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Joe,
Again, I'm with you on 3 tons for this app, just a bit concerned about predicted 3800 hours of winter runtime. Suppose, thinking 'out loud' so to speak if y'all up there start heating about now in September and do so into May the hours might look like this:
Sept 50
Oct 150
Nov 250
Dec 350
Jan 500 (16 hours per day)
Feb 425
Mar 300
Apr 200
May 50
That adds up to 2275 winter hours. Pushing that up to 3800 implies near continuous operation Dec-Feb and quite a bit of aux heat after dark for several months.While I agree aux heat isn't the enemy, it ought to be a friend who visits moderately often, but not a roommate there every day.
If I'm way off base on this let me know...
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engineer
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| 09/23/2009 9:19 PM |
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Ducts off the end tend to grab all the flow at the expense of side ducts
17 seems a tad high for crossover to aux. From what I recall, it is below 17 for quite a long time in Canada every winter, even in the mild "southern" parts. (Why I moved from Boston to Florida)
Joe really is the better guy to pay attention to in your climate - I'm along for the educational ride.
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Without data, you only have an opinion. |
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newdeal
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| 09/23/2009 9:52 PM |
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| near as I can tell there are about 1522 hours per year of continuous operation...it would start operating continuously around 31 degrees. so basically that is two months in the winter of constant function. The 4 ton unit on the other hand a 4 ton unit would be operating continuously for 605 hours...that is of course if I am reading the bin analysis correctly...it may be more i just added up all the numbers of hours that said 100% at that temperature, at 32 degrees it was 94% of the time running for the 3 ton so i didnt add any hours because i am not sure if the hours go up or down...like at 32 there are another 694 hours so if i needed to include those then it would be over 2200hours continous running for the 3 ton. |
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joe.ami
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| 09/24/2009 10:54 AM |
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Again I'm yeilding to software that notes you climate as slightly warming than mine for some reason. In the absence of first hand experience I trust the local opinions.
The data before me is only one bidder actually did a load calc. That bidder uses the same software as me and selected the same unit I would for my "cooler climate".
If you are able to verify good references for the guy.........
You might ask him to quote you a 4 ton with required duct mods and compare the difference. You might find that pay back is 10, 20 or even 30 years for the upsize vs extra aux. use.
I have no ego in this and want you to be happy with your investment. Take mine as an opinion of some guy with no experience in your area but lots of experience in geo. Bachelor #4 so far sounds like the most professional of your choices.
joe |
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newdeal
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| 09/24/2009 6:37 PM |
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| Do you think that going with a 4 ton unit for piece of mind is a bad idea I would like to ensure it will keep my house warm and not have to worry that the numbers are a bit off. If the three ton numbers are off by a little it will make a huge differance on the amount of aux heat needed. I listed my ducting what would I need to do to get the ducts to be adequate and can't I just set the fan to slower speeds I see that the fan is adjustable |
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