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  1. #14
    Join Date
    Apr 2006
    Posts
    12
    comfortdoc, thanks for the reply. The heatpump I'm looking at would be an add-on to my LP forced-air system. It's a 5yo Trane, single stage 80,000 92%. My 10 SEER 2.5ton A/C would be replaced by the HP. I have one quote for a Bryant HP (same dealer than installed my current setup) and the cost is relatively painless due to a $600 credit from my power company. I'm looking at $2.00/gallon LP vs $.09/kwh electric that has a stable price here in Ohio. If I save 50%, I'd have a payback in about 2 years even if I replace the coil. The installer stated he might be able to replace a piston in my Trane coil and it would work but I've seen posts here that say that's not a good idea. Still researching that one.

    As for the house, it's 140 years old, but I've updated a very substantial part of it. Windows & doors are new, many rooms have been gutted and walls insulated. Attics are insulated properly, but I have some venting improvements that could help with cooling. About 50% of the first floor is crawlspace and I do plan to update the floor insulation this fall. The only other real project will be filling the remaining wall cavities (less than 30%) when I install new siding next year hopefully. Most of this has occurred since the last load calc. Duct systems are a little hit-miss due to the age of the house and how some of the lines have to run due to crawlspace. Obviously, this place didn't have forced air when it was built!

  2. #15
    Join Date
    Jul 2000
    Location
    Louisiana , USA
    Posts
    3,280
    Originally posted by skinny2
    We were spec'd for right between a 2.5 and 3 ton A/C. Due to the way our house heats up, room for loss improvements, humidity, and general temps here in Ohio, we went for the 2.5 ton system. This was 5 years ago. No problems to mention with this system, always keeps the house comfy although it certainly has limits. It has been unusually hot lately and there have been a couple days the A/C has run non-stop to maintain 75 inside. It has fun stright for over 12 hours on some days. Usually, the system runs a lot which was desired for humidity control, however it normally cycles when the temps are below the mid-90's.

    I guess my question is....Is it bad for a system to run non-stop for long periods of time? Granted, I probably couldn't cool the house to 72 with this system, but I don't think anyone would want to. Our electric only goes up about $50 in the summer so even though it runs a lot, it's not costly. Any thoughts on upsizing the coil while we're modifying the system? I personally don't want to, but we may sell the place in a 5+ years and wouldn't want any problems from something like this.

    This is Turtle.

    Is your hvac system keeping the temperature where you want it to be all year round ? If so , leave it alone.

    Running 24 hours a day is not a bad thing at all in very hot weather. The HVAC system only has 2 speeds [ off and running ] .

    Running too much does not kill a hvac system but poor maintaince will kill it.

    TURTLE

  3. #16
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274
    Originally posted by John Lloyd
    tigerdunes: obvious why there is no 'professional' next to your name. Now don't get testy, but virtually ALL the answers you gave were wrong. At least you indicated it was your opinion and only that. You are getting 'personal' though when you state "the dealer did you a disservice by installing a 2.5 ton." Nothing could be further from the truth!

    For your information, having virtually ANY electrical applicance on and running is less wear and tear than having it kick on and off over the same period of time. If a system is 'properly' sized, then when it is under high load conditions it should run virtually non-stop. The key to this is the fact that it is continuing to satisfy the thermostat requirements. That in and of itself would not indicate an undersized system.

    For the same reasons you are wrong in your assesment that the life of the equipment will be shortened. In fact, it may prolong the life of the system or at least minimize mechanical failures.

    You one observation that the ductwork should be checked is correct. (I believe in giving credit where it is due.) Although 1/2 ton in size is not critical, it would be conscientious for the contractor to verify air supply and return to maximize the operation of the system. It certainly would not hurt to do so.

    But soulds like midwest said it all as well. Unfortunately, someone out there will listen to what you are saying and believe it to be the truth. Advice such as yours is what keeps our industry and service departments busy. All the best, John
    A G R E E D !
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #17
    Join Date
    Feb 2005
    Posts
    46
    Ugh! Sometimes I just feel compelled to respond...this doesn't seem like rocket science.

    A properly done Manual J is done for DESIGN temps. In other words your system should be able to hold a given inside temp at a given outside temp - plain and simple. For AC that outside temp should not be the hottest temp on record since 1888 nor should it be anything less than average.

    Choosing an average high temp and a desired indoor temp SHOULD result in a properly sized system running constantly to satisfy the required inside temp. A lower temp will cause the unit to cycle <since it's sub maximum load> and a higer temp will just mean the system can't keep up. Does that mean your house will be 98 degrees when it's 98 outside and you only designed it for 95 - NO. The highest design temp is only reached during a minority of the day (in other words if you design for 95, it's only really 95 out for the hottest hours in the afternoon). This brings up the point of heat infiltration or heat gain. If the system is designed for 95 outside and 75 inside and you get a day of 98, the actual time your system will not be able to satisfy your demand may only amount to a couple of hours since time outside above 95 is only a few hours and it takes time for the heat to infiltrate your house.

    By continuing to improve the insulation in your house you are reducing the heat gain and thus upping what the outside temp can rise to while maintaining the indoor temp. Conversely, it means you could also maintain a lower indoor temp.

    Just remember, cool and clammy IS NOT cool and comfortable so remember to factor in dehumidification into the equation. Bryant's evolution controls and system do a great job of this.

    Just a shout to BaldLoonie - he's a great guy and won't steer you wrong BTW, he also works for a darn good company that has a solid reputation in our area - that's a combo that's hard to find.

  5. #18
    Join Date
    Jun 2006
    Posts
    21
    My Experience....

    We bought a new "old" house, it had a 2.5 ton A/C. During our first summer in the house, I noticed that on the hottest days, the unit ran like a champ, cycling on and off regularly. But on days in the 80's, the unit would cycle more frequently, but the humidity in the house was alot higher. Even though the unit was holding 75 F in the house all the time, it just wasnt comfortable because of the raised humidity levels

    Last spring I decided to install a HP. I doubled check my manual J calculations (called for 27,000 BTUs of cooling) and went with the smaller (2 ton) unit. Yes, my unit has been running alot these last two weeks, but since most of the heating season is spent in milder temperatures, I am more comfortable more of the time.

    I have been in this business 18 years, and have always known that the hardest thing on motors is when they start.

  6. #19
    Join Date
    Feb 2005
    Posts
    35
    Originally posted by tigerdunes
    And a unit running continuously will drive up one's electric usage.
    I disagree, I live in a new cookie cutter neighborhood. My neighbor has a very similar house, and has a 4 Ton unit. Load calc said I only needed 3, so I talked the builder into only going 3 instead of his 4. My unit ran 100% of the time during the day during this heat wave, vrs theirs which cycled. My electric bill was over 30% cheaper.

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