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  1. #1

    questions about replacement system, sizing, options

    Greetings,

    Our gas furnace (80%, forced-air) and gas water heater are ready to be replaced (I had them installed in 1992), and we're shopping for as much efficiency as we can afford, aiming at a heat pump if possible. Because we're looking for efficiency, I've been asking contractors about inverter-driven heat pumps like the Carrier Infinity Greenspeed, also Daikin or Mitsubishi are candidates. We've looked into geothermal systems (jealous of the one that one of my siblings has), but have both space and financial constraints. Can't afford one of those Daikin Altherma systems, either....

    A little background: Home is in Oregon (Portland area), built 1978, 1890 sq ft of conditioned space, 2 floors. Upper floor is all living area, lower story is garage, laundry, family room (finished walk-in basement). We've recently had attic air sealing done and attic insulation added, and have done some window sealing, current CFM50 number is 1800 (down from 2900 before we did all the sealing work). Energy audit report thinks we have 17000 BTUH heat load, 23000 BTUH cooling load, after all our improvements (modelling software used was Recurve).

    One contractor's load calculation came up with 26250 BTUH for heating, 23600 BTUH for cooling. They initially recommended a 3-ton Greenspeed heat pump, but were willing to go with a 2-ton unit when I asked. Another contractor came up with a 2-ton size for the Greenspeed heat pump, so I'm beginning to think that's in the ballpark of a correct size. A couple options included 2.5- or 2.6-ton Daikin inverter-based systems.

    As an aside, our last 2 years of utility bills (combined gas & electric) have never exceeded 17000 BTUH equivalent. In the cooling season we've been using a couple 5500 BTUH window air conditioners for a few hours on the hottest summer evenings until we can open windows and use portable fans to cool the place down, so are looking forward to being more comfortable on the few hot days or weeks we get here.

    Before our air-sealing & insulation work, we ran our furnace fan all the time, due to dust allergies in the household (old system has a Honeywell electronic air cleaner, though I replaced the cells a year or two ago with a 4" media filter). Once I discovered how much money the furnace fan was costing (at about 390 watts measured), I installed a fan timer to cycle it on only 35% of the time. We've been running this way about 4 months, and discovered a "new" problem when the weather got warm here (80-90F) for a few days. Without the fan running all the time, there's a big temperature difference between upstairs and basement (big difference in solar gain). So upstairs, where the thermostat is, it could be 70-75F, thus heat never comes on (setpoint is 68F), but it still feels pretty chilly in the basement. We didn't have much of a difference, if any, in the full-on heating season, so now we're thinking about zoning the basement at the same time that we replace our systems (and especially since we'll have central air-conditioning with the heat pump system, as there's a big diff. in heat gain between the two floors).

    Another aside: Our old furnace is way too huge (110000 BTUH input), but it looks like nobody makes a gas furnace small enough for our load anyway. I originally thought we could get a 90%+ gas water heater and use that for backup heat in a variable-speed air handler, but there is no such beast from Carrier to match with the Greenspeed H.P. So Plan B is to go with an all-electric air handler, though I expect we'll seldom need backup with an inverter heat pump in our mild climate.

    I know that's a lot of verbiage, but from reading this forum I gather that you all like having lots of background info rather than having to do a bunch of guesswork. So now I come to some questions about air handler, sizing, zoning, and alternatives.

    (1) For the best HSPF ratings, the charts show matching a 2-ton
    Greenspeed outdoor unit with the 5-ton air handler (I can't see
    any matching gas furnaces that give the HSPF of 13). Are there
    any down-sides to using the -006 fan coil with the 2-ton condenser?

    (2) Am I nuts for going with a 2-ton unit here? My thinking is that a
    3-ton unit will not be able to ramp down low enough (40% of 3 tons
    vs 40% of 2-tons) in cooling season, especially if we go with 2 zones.
    We do have a fireplace and a wood stove we could use if there's an
    extended spell of colder-than-usual weather (if we want to avoid
    hitting the expensive heat strips). The "shoulder" heating seasons
    don't need much heat here either, and I'd be concerned that a
    too-oversized unit would be cycling on & off (and again, even more
    so if we add zoning). Am I off base with the above?

    (3) We've got a couple of prices on the basement zone, and also an
    alternative solution (below). Is zoning likely to be more expensive
    to add on later, as compared to doing it at time of installing the
    new system?

    (4) One proposal recommended a Daikin slim-duct system, with four
    zones sharing one outdoor unit. I think this is a VRV-III system,
    and the cost is in line with the Greenspeed split system without
    zoning. My main concern with this approach is the relatively low
    HSPF numbers (around 8, 8.5, or 8.8, depending on indoor unit),
    and loss of central air purifier options. Any opinions?

    (5) I've been asking contractors about a 100% outside-air economizer,
    to use for night-time cooling/purge of the house. I work with
    computer datacenters and in our climate using outside air instead
    of air conditioning is real big right now. We do pretty much that
    with our house now, but pollen allergies and security concerns make
    it tough to do that with just open windows. I'm aware of the
    NightBreeze system, but that won't work with the Greenspeed
    heat pump. So far contractors have been reluctant to quote on
    this type of system, unless I can find something to buy and pay them
    to install. Any suggestions?

    Thanks!

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,085
    How many 5500BTU window units have you been using? If 4 or less, then you know that a 2 ton will cool your house fine.
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    How many times must one fix something before it is fixed?

  3. #3
    How many 5500BTU window units have you been using? If 4 or less, then you know that a 2 ton will cool your house fine.
    Thanks for the question.

    Last summer, we used just two, but that's 'cause we gave up on trying to keep the entire upstairs comfortable. So one 5500BTU unit went in the basement (where we hang out if it's hot upstairs), and the 2nd went in the master bedroom.

    In prior years, we used one portable 11000BTU unit in the living room, and one 5500BTU unit in the master bedroom. The living room would still get up above 80F on the hottest days (95+). But we added attic insulation and did a lot of air sealing (as I mentioned) in December, so this summer will be the first we've experienced with that in place.

    However, I'm not too concerned about 2 tons being enough for our cooling load. All three load-calcs we've had indicate it should be plenty, and as you say, experience with the portable/window units confirms it, plus we're not heavy consumers of cooling anyway. My only worry about cooling is that we not end up making the basement too cold in the summer, on the less-extreme days. We've had a couple days this month where we wanted cooling upstairs (it got to 77F inside), but the basement remained cool enough (68F). That's why we're asking about zoning.

    On sizing, I'm more concerned about the heating side, since we've gotten a lot more variation on the heat load calcs. I don't want an oversized unit, nor do I want a surprise on our electric bill if we hit the heat strips on a marginal-sized unit. If I understand correctly, a 3-ton unit can only ramp down to 14400BTUH at its lowest, while the 2-ton unit will go down to 9600BTUH. The majority of the heating season is well above the 24F design temp in use at our location.

    Thanks.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,085
    Find out what the BTU output of the 2 ton is at say 17 outdoor temp.

    Zoning can help a lot in both heating and cooling.
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  5. #5
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    If you only need 17,000 Btu's for heating then a 2.0-ton Carrier Greenspeed or Bryant Evolution (same unit, different name) system is ideal. No problem with the nominal size of the air handler as long as it's a matched unit to the 2.0-ton outdoor unit. Duct system must be carefully designed so that it performs properly with zones and variable speed HP. Your brother will be jealous because your HP will cost a lot less than his and will perform better. By better I mean your variable output will be better than his 2-speed output and given the stability of your air temperature, you don't need the constant Btu output of a geo system. These new variable speed units are quickly changing the way the industry provides heating options to clients and woe to the companies that aren't keeping up.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  6. #6
    Find out what the BTU output of the 2 ton is at say 17 outdoor temp.
    With the 006 fan coil (HSPF of 13), the AHRI directory says you get 24800 BTU at 17F outside. Oddly (to me), it only gives 23600 BTU at 47F outside.


    Zoning can help a lot in both heating and cooling.
    Yes, it's desirable. But finances are limited; We're trying to figure out if adding the zoning later will cost huge amounts more than doing zoning now (at time of system replacement).

    Thanks for the note.

  7. #7
    If you only need 17,000 Btu's for heating then a 2.0-ton Carrier Greenspeed or Bryant Evolution (same unit, different name) system is ideal.
    Agreed. What made me nervous was one load calc that showed 26600 BTUH.


    No problem with the nominal size of the air handler as long as it's a matched unit to the 2.0-ton outdoor unit. Duct system must be carefully designed so that it performs properly with zones and variable speed HP.
    Duct system is already existing, so "design" is probably wishful thinking, except for any new trunk to our basement if we do a 2nd zone. Evidently the Greenspeed outdoor unit communicates with the Infinity air handlers to coordinate fan speed with the compressor & condenser fan speeds, etc. They tell me it'll be fine with our ducts as they are.

    Your brother will be jealous because your HP will cost a lot less than his and will perform better. By better I mean your variable output will be better than his 2-speed output and given the stability of your air temperature, you don't need the constant Btu output of a geo system. These new variable speed units are quickly changing the way the industry provides heating options to clients and woe to the companies that aren't keeping up.
    That's what we're hoping (:-). He's pretty tickled with his geo system, though. He says his electric bill is unchanged, and he no longer has the $200/month oil bill for running his old oil furnace in the winter. It helps that his solar panels offset what little electricity his system uses.....

    Thanks for the reassuring comments.

  8. #8
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    1,991
    Chronian I am in your area if you would like another analysis of your system. We perform full Manual J load calculations and can often match greenspeed pricing for geothermal systems if you have a 5,000 sq foot or larger lot. We are a 32 year old company here in Portland. Our website is my username and my name is Travis if you have any questions.

    As for your questions, it appears that a 2 ton system with an invertor should be fine for the house but without doing my own load its hard to say.
    If you have allergies you could use a fresh air economizer that drops fresh air in before a media filter or electronic air cleaner or possibly an HRV system depending on your needs.
    Often times the Daikin or Mitsubishi systems show a very low HSPF even though in my experience they are just as efficient as systems like the Greenspeed. The difference is that we have Daikin and Mitsubishi systems that are 8 year old invertors while the Greenspeed is a new product.

    Here is a Mitsubishi with air handler system we installed a little over a year ago and this customer absolutely loves his system, however they only come in 3 and 4 ton options.
    http://youtu.be/ZrCId6XNkR4
    If you are curious about a ground source heat pump we can horizontally bore for a ground source heat pump and add a split system in and as stated above, we are typically about the same cost as a greenspeed for this after tax credits.
    http://youtu.be/2vVOpamKz_c
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
    Like us on FACEBOOK if you like our advice here!

  9. #9
    Hey, I just wanted to thank you all for the information you've shared. I've managed to get all my questions answered, and really appreciate the time you folks have taken to help.

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