Do I really need a heat pump?

Discussion in 'HVAC Heating & Cooling' started by mar3232, Dec 24, 2011.

  1. mar3232

    mar3232 New Member

    Messages:
    87
    Location:
    Indiana
    I want to ask you gurus something.

    First of all, I hate hot weather, don't mind winter, so cooling is important to me. I want better more reliable air conditioning than I do heating. My house is very well insulated, a single story, brick only 1600 sq ft and I can actually turn my heat off on winter nights and stay comfortable.

    Unless it gets below 20 or so. I have some great south windows and also plan on a wood stove next year, so like I say -- screw the heater.

    Right now, I have a TRANE heat pump that needs a new compressor, so I've been using the auxillary heat on the furnace once in a while but mainly, a
    1500 watt space heater and I feel fine.

    BUT --

    I friggin love air conditioning and when it's over 80 here in the midwest, I'm miserable.

    I have a lot of fans to help keep things dry, like I say, a well insulated house but I'm surrounded by woodlands and close to a river so it gets damn humid around here.

    So, tell me what I should do.

    Do I really need a heat pump?

    I do want to save on my cooling costs so I would rather spend more in that department for 2 reasons --
    (1) It's power consumption and efficiency factors and
    (2) RELIABILITY

    Every AC I've ever owned has ended up with a bad compressor after 5 years or even sooner and seeing as no one will just replace a compressor and I'm not a licensed contractor, I have to shell out big bucks for a new condensing unit.

    &^%$ that.

    I do like to save money anywhere I can so should I stick with a heat pump?

    Is my system adaptable to doing something else? Especially considering my desire for some quality AC? What would you do?

    The TRANE outdoor unit is 2twb0030a1000b

    the furnace is twe031e13fb1

    thanks for any help on this.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    Most heat pumps either don't work or are very inefficient at low outside temperatures, then, they use the auxilliary electric resistance heaters. A wood stove can be used for primary heat, but is problematic if you're going to be away on vacation or extended times in the winter. If I had to guess, your a/c unit is probably oversized and short cycling which is why it has such a short life. They should last longer than 5-years. Bigger in an a/c unit is not better. Ideally, for maximum dehumidification, the unit would run constantly. Since all days are not the same, a two stage compressor and a variable speed fan can go a long way to adjusting to the daily need and provide best comfort level.

    You need to do a good heat load analysis to determine the needed size of the a/c unit. A heat pump may be good for your minimal heating needs. Personally, I don't like the typically cooler outlet temperatures of a heat pump verses a furnace. But, I like my radiant heating system better than that.

    Trane is generally a good brand, but the quality of the installation and the proper sizing of the unit can make a huge difference, regardless of the brand selected.

    Sometimes, the choice of heat depends on the energy available: oil, gas, propane, electric, and their relative costs.
  3. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,841
    Location:
    NW Ontario, Canada
    Jim, you are assuming an air to air heat pump. Around here, heat pumps are closed loop ground source, or closed/open loop lake source or well water source.

    Our situation is the reverse of the OP. A/C is optional and heat is essential. I heat primarily with FA gas but supplement with about 4 cord of wood. You are correct that the choice of heat often depends on the available energy source and their relative cost, but for me wood heat is a lifestyle choice more so that economic.

    A/C for me is an economic choice and so far I've been too cheap to put one in.
  4. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE
    Regardless of whether you get straight AC, or a heat pump, spring for a scroll compressor.

    MUCH quieter, and I believe they last longer.
  5. DonL

    DonL Jack of all trades

    Messages:
    3,819
    Location:
    Houston, TX
    I know that this does not answer your question,
    Why do you think that your compressor is bad ?

    You should have gotten many more years of service from that unit.


    When I lived in Indiana having Air conditioning was a unneeded Luxury. Even in an Automobile.
  6. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    get 2 more 39$ oil radiator heaters and a few 99$ window AC's. Your all set for nearly free.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    Ground source heat pumps are a good way to get heat, but can be quite expensive to install. If you can reuse the inground stuff, it makes sense to do so. Air-air in a cold climate is probably not a great choice. Personally, I don't like high humidity, regardless of the temp, so run my a/c during most of my summer. Keeps the excess pollen and dust out of the house, too.
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    With a Trane , you don't really get to "OPT" for a different compressor. Even if you are beyond warranty, no reputable Trane tech would put in anything but the Trane-recommended one. On the other hand, it may very well already BE a scroll.

    You can get the compressor replaced for a lot less than a whole new unit. The compressor will be pricey ( R22 compressors are going UP!). But assuming you are an R22 system, Trane is not making dry22 units, so you would have to upgrade to R410, meaning a change of indoor coil, or at a minimum the expensive flush.
  9. Runs with bison

    Runs with bison New Member

    Messages:
    891
    Location:
    Midwest
    So you have a Trane heat pump with electric strip heater back up? Resistance heating by itself is very inefficient, so I wouldn't recommend skipping the heat pump, particularly if you think you might ever sell the home.

    If I'm reading the info right parsing the Trane model numbers, 2 stands for R-22, T = Trane, W = Split, B = basic, first 0 = 10 SEER (very low these days), second 0 = 1-6 tons, 30 = 30,000 Btu/hr or 2.5 tons. New AC units typically use about 33% less juice than the older low SEER units--I confirmed this over the summer on my replacement AC unit.

    Since your unit is R-22, assume that you must replace everything. There are some flush kits for converting to the new refrigerant, but I doubt your old system is worth keeping, particularly since you are having frequent failures. Have you noticed any refrigerant leaks (having to top it off once a year or so?)

    Seems odd that a compressor is failing after only 5 years, but I've never had a heat pump. Is it working too hard in winter? I'm wondering if the point at which aux. furnace heat kicks in is too low...making the compressor run a lot harder. I would expect the compressor to fail much sooner on a heat pump than on AC, but 5 years is awfully short.

    I agree with others about the ground source bit, you don't see them much around here because the ground source is so incredibly expensive to install.
  10. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Since it is a 10 seer unit, it is NOT POSSIBLE to install just a new heat pump unit. It will not operate on the SEER differential. If you install JUST a condensing unit, a tech who knows what he is doing can make that work, but you will not get full advantage of the outside units 13 SEER.

    Compressors fail, but if on average you should not be failing in under 5 years. First, that repair should be a warranty. Second, you should consider finding a new installer, because they are probably not observing all best practices, or you would not have these problems. THIRD....any condensing unit or heat pump is repairable, and under 10 years is "young" so for them to say you cannot repair it...they are just taking you to the cleaner. Now, a compressor if not on warranty will cost you 1/3 to 1/2 the cost of the whole unit, and there is a lot of work. So economically, it is a decision point.
  11. mar3232

    mar3232 New Member

    Messages:
    87
    Location:
    Indiana
    I had a quote of $1600 to completely replace the outside unit and was going to do it but I placed 3 phone calls to the guy (an authorized Trane dealer), simply asking for the model number of the new unit, and he never called me back.

    I'd really like to just get the compressor replaced because the unit is not that old (I inherited it when I bought the home 2 years ago) -- so if anyone ever sees this and is close to central Indiana, please let me know how I can contact you.

    One other question --

    I noticed that there are times in the winter when the compressor "tries" to kick on but obviously when it's too cold, it goes to the auxillary.

    Wouldn't that be hard on a compressor?

    Wouldn't it be better if you KNEW it was going to be below freezing (or whatever the right cut off would be) -- to just go ahead and manually switch the thermostat to auxillary? So the compressor wouldn't have to go through the agony?

    Would that be a good practice?
  12. DonL

    DonL Jack of all trades

    Messages:
    3,819
    Location:
    Houston, TX
    Yes it would , and that sounds like the Compressor heater may not be working.
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    The thing should know if it is too cold to do any good and not even try to turn on. But, as said, if the internal heater isn't working, you could have ice inside and that would make things problematic.
  14. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    So the boiler guy has to keep us on message.

    Ground source heat pumps are efficient in terms of converting energy, but the cost of installation for modest homes/loads is prohibitive. The relative importance of cooling vs. heating has no baring on the type or conversion efficiency of the cooling system. Any combination of heating and cooling will compromise both. So if it is cooling we are after a scroll driven air-to-air heat pump is the obvious choice providing good efficiency, reliability and cost of operation. As mentioned the heat/cooling load is the first and most important step since an over-sizing cooling system (regardless of type) will fail to decrease the humidity - the main cause of discomfort in warm weather.
  15. Dana

    Dana In the trades

    Messages:
    2,790
    Location:
    01609
    In an Indiana climate the efficiency of ground source heat pumps aren't super-dramatically better than R410A refrigerant air-source units with (very quiet) continuously variable speed scroll compressors, and can even be met or beaten on average efficiency by ductless split-systems with continuously variable speed blowers. In the same climate a ductless mini-split/multi-split in heating mode would hit a heating season average COP of between 2.5-3.0 without use of any auxilliary heat. If you like the cold and keep it only 60-65F indoors you'd even beat that. (For identical cash-outlay you could buy enough rooftop solar panels with the difference in system cost to more than make up any marginal seasonal efficiency shortfall between a mini-split and ground-source heat pumps in that climate. It depends somewhat on which has better state/federal/local subsidies.)

    By virtue of being fully modulating systems with a turn-down ratio greater than 2:1, you can safely oversize them by ~2x, which also increases their average heating-season efficiency. (This is because they run significantly higher efficiency at low-mid compressor speed than at max.) Most of the better ones have a full-system rated mid-speed COP of ~2.7 at an outdoor temperature of +17F, and would still be above 2.0 @ +5F. To get the most out of them it's better to use a "set & forget" strategy rather than setbacks (either in cooling or heating mode), since the lower efficiency they would have during the recovery ramp ends up being more total power than if run at low speed in temperature-maintenance mode. Many have a "dehumidify" mode too, which maximizes latent cooling (drying) rather than sensible cooling.

    Ducted systems are rarely as flexible, but with variable speed scroll compressors can hit a system average COP of 1.8-2 in heating mode in an IN climate when carrying the whole load. (no aux heat). By contrast most ducted R12 & R22 systems hit a COP of 2 in heating somewhere in the mid-20s F, and that's even without factoring in the air-handler power, and oversizing them makes them run less efficiently with lower comfort and higher maintenance costs. (And reciprocating compressors are louder too.)

    Ducted or ductless, any R410A refrigerant heat pump with a scroll compressor and a variable (or multi-) speed air handler will be more comfortable, quieter, and more efficient than what you've been living with.
  16. mar3232

    mar3232 New Member

    Messages:
    87
    Location:
    Indiana
    Thanks so much -- great forum -- nice to see one devoted to HVAC like this.

    I printed out this info and want to share it with a pro this spring and decide what to do.
  17. mikeinkirkland

    mikeinkirkland New Member

    Messages:
    12
    Location:
    Kirkland, wa
    A heat pump over central A/C is a really minor upgrade. With most modern systems it's literally a $10 (mfg cost) valve and a couple of control circuits to reverse the system for heating.

    Modern heat pumps have huge benefits over resistance heating (of any sort, furnace, baseboard, portable heaters, etc.) to the tune of 1/4 the operating cost at outside temps down to 40F or so. A typical house in 40F weather might need 25 KW of electric resistance heat but only 6 KW to run a heat pump to deliver the same amount of heat.

    So, IMHO, the added $500 or so in cost for a heat pump over a similar capacity A/C system will rapidly pay for itself. The only time the math gets tricky is if you also have cheap natural gas and are willing to pay for a high efficiency gas furnace. In that case the gas is usually cheaper below about 45F but the heat pump still wins above 45F.
  18. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE
    This got me to thinking about where to set the balance point on my system. Factory default is 20 degrees F and I have kept it there. A couple years ago replaced gas furnace with high efficiency unit and never thought to raise the balance point.

    What is cheap natural gas? Currently my utility charges $0.45/therm - but I have no idea if that is cheap or not. Should I raise the balance point to 40, 45, or something else?
  19. mikeinkirkland

    mikeinkirkland New Member

    Messages:
    12
    Location:
    Kirkland, wa
    You have really cheap gas! We're paying about $1.07/therm. Depending on your electric rate you should probably be using gas below 45 or even 50F.

    A Therm is 100,000 BTU/H. With a 82% furnace that's 82,000 output or 24 KW/H of electricity. At .08 per KWH that's $1.92 for the same amount of resistance heat. So if you're really paying only $0.45/therm, that's a factor of 4.3 ($1.92/$0.45)--meaning the heat pump has to be running at 4.3 net COP to break even (you have to do the math if you're using HSPF). You would need the performance tables for your heatpump to figure out the crossover temp. And even that can be optimistic if it doesn't factor in defrost cycles, other losses, etc.

    Here in the northwest 40F is pretty common, sometimes 35F or 45F. It really depends on your energy rates and heatpump. The newer and higher-end models have much more intelligent defrost capability and can maintain more efficiency at lower outdoor temps. The older/cheaper ones use a rather simple "dumb" defrost that will always have the system flipping into defrost even when it's not needed. With their smaller coils, etc, they're also less efficient even when they're not in defrost at low temps.
    Last edited: Feb 12, 2012
  20. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE
    Great info mikeinkirkland!
    Thanks

    Other advantages of using the gas furnace in our case include the fact that I like the warmer air temp coming out of the registers, and it is easier to humidify warmer air at the plenum. I am going to set the balance point at least at 40 now based on this.
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