Old Heat Pump - New Options??

Discussion in 'HVAC Heating & Cooling' started by devans175, Nov 6, 2012.

  1. devans175

    devans175 New Member

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    Maryland
    I live in Maryland. I own a large rancher. Most of the main floor is heated by a hot water boiler. I also have a 12x30 addition that is heated and cooled by a heat pump. The heat pump also has a 10 inch return and 2 6 inch supply ducts running to the basement. This set-up has done a good job thus far of cooling these areas and removing humidity from my basement. My complaints are, like most people I talk to, I hate the heat pump for heating. It's noisy, uncomfortable and expensive!! It's really old and I think the fan went bad before I left home this past summer for Afghanistan (I'm in the Air Force).

    Are newer heat pumps any better than the 10-15 year old "Comfort Maker" that I've got? If I do replace it with a new, high efficiency model (should I), what are some low cost, yet efficient means to add supplemental heat to the rooms when the temps drop? I was thinking of adding some electric baseboard heat, but I can't get a feel for how efficient they are compared to the heat pump. Does this make sense? I'd love sume ideas from you all before I search for contractors when I get home next month!!!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    A heat pump is generally in the order of 2-3x better at generating heat than a straight electric baseboard heater...IOW, for 1Kw to run the pump, you get the equivalent of 2-3Kw of heat out from the heat it can extract from the air (or ground or water, depending on the type of heat pump).

    The fan speed used for cooling may often be to high for comfortable heating, adding to the noise, and preventing the air from warming as much as required to feel good coming out of the ducts.

    You might consider one of the newer split systems which are both quiet and efficient.
  3. devans175

    devans175 New Member

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    Location:
    Maryland
    I'm familiar with the split units, I like them and I will definitly consider them. The one place I think they fall short is that they don't move the air around as much. I like the idea of turning the air over in the basement, which is all below grade.
  4. jimbo

    jimbo Plumber

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    Your old unit is at best 10 SEER. A newer unit will be 13 SEER minimum, and 14 to 20 SEER are available. A heat pump is the least expensive heat often, but is not always a "comfortable" heat.

    To upgrade to a new Heat Pump, you will have to also replace the indoor air handler, as a proper ARI match probably cannot be achieved...meaning you won't be able to set subcool for proper operation.
  5. devans175

    devans175 New Member

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    Maryland
    I was afraid of that. It's probably best to replace them both anyway. The old system was put together pretty pooly. If I do go with the heat pump option, is there a good option for suplemental heat.. is there such a thing as a "High Efficiency" electric baseboard?
  6. Dana

    Dana In the trades

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    Combining the heating & cooling functions with a ventilation function may save something on up front cost, but isn't always rational and costs more to run over time. If the basement and addition are basically two relatively open spaces you can heat & cool/dehumidify them with a 2-head ductless at extremely high efficiency and low noise. Ducted air heating & cooling systems exchange the air, sure, but they also drive outdoor air infiltration at uncontrolled rates, which adds to the heating & cooling loads.

    Ventilating with an energy recovery ventilation system (with it's own small diameter ducts) is a lot quieter and guaranteed more effective way to remove indoor air pollution. In most homes a complete whole-house ERV system will run $2-4K- not free, but the difference in air quality in the home is almost immediately noticeable, and if properly installed as a balanced system, only moves air through the heat exchanger, not random leakage places in the house the way unbalanced and leaky ducted heating/cooling systems do. The sizing of your existing ducts may be amenable to using them for the ERV, with adjustments.

    In a MD location a good inverter-drive ductless will have average a coefficient of performance over 3, (maybe over 3.5) during the heating season, and may be cheaper than running a gas fired boiler (depending on your actual gas and electric rates.)

    There is no such thing as a high efficiency electric baseboard. They all run at a 100% (COP=1). A ductless will use less than 1/3 the amount of power. Your existing heat pump may be only averaging a COP of 1.5 in a sub-optimal implementation, and it's more than likely not well balanced in heating mode between the basement and the above grade addition. With a 2- head ductless you could zone the basement and addition separately, and you may be over-heating the basement much of the time on a single-zoned system, since the heat loss characteristics are so dramatically different from above-grade rooms.

    You could just ventilate the basement as part of the ERV system, and use a room-dehumidifier if it's ever necessary, leaving the basement only semi-conditioned, and go with a much cheaper single-head ductless. A 3/4 ton or 1-ton single-head ductless mini-split can run under $2K as a DIY install, under $3.5K if you hire a pro, and is probably sufficiently sized for the task. (There are people who heat their whole house with a 1-ton mini-split in comparable climates to yours, but it really depends on how the addition is built.)

    Oversizing a ductless by more than 50% for the actual loads isn't advisable since it'll lose efficiency to cycling and they'll be louder, but at 1.25 oversizing they do quite well, since they modulate with load and run every long cycles a very low compressor and blower speeds, and very low power. To get the most out of them you "set and forget" the temperature rather than turning them off or setting back, since they would have to run at higher speed/lower efficiency on the recovery ramps, using more net power than the savings from an overnight setback. Heating with ductless is nice- very comfortable. Once you've done it you'd never go back to a ducted air source heat pump solution (except maybe the best-in-class fully modulating versions.)
  7. jimbo

    jimbo Plumber

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    Electric heat is virtually 100% efficient....all the KW are converted directly to heat. It is just that electricity is so costly compared to nat gas, or even oil.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    22,139
    Location:
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    The heat pump gets much more heat out per Kw than just using electricity in resistance heating. With the modulation, the air is likely to move over the heat exchanger slower, making the output air temp higher than with a more typical heat pump with an air handler.
  9. devans175

    devans175 New Member

    Messages:
    66
    Location:
    Maryland
    I think I'm sold on the ductless system. Incidentaly, it is the most common form of climate control in my current location (Bagram Afghanistan) We call them Chigos, because that's the main brand you see over here. That should be somewhat encouraging to potential buyers, since the conditions are absolutly brutal and they seem to last, even with minimal routine maintenance!! I'll see how it works and consider the dealing with ventalation seperatly. I'll most likely go with a contractor install, but I like to do some homework in advance. The above ground addition is about 360 SF, so my research shows a 9000 BTU unit should be good there. The other part of the space I want to condition, my basement, is 1000 SF. The charts I found say that's 20000 BTUs. How much can I shave off, considering the fact that the basement is entirly below grade and the teperatures are fairly stable most of the time. I want to make sure the thing isn't oversized so it's able to deal with the humidity effectivly. I know a true load analysis includes a lot more considerations, I'm just trying to get the basics so I can talk intelligently to the contractor and make sure that he knows what he's talking about. Also, what is a good model that offeres a good programable thermostat option..or better yet, can I just use a standard, off the shelf Honeywell programmable thermostat?
    Last edited: Nov 8, 2012
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    Just using sq ft and a generic figure will likely oversize the thing, which costs more to run, buy, and affects the comfort levels, too. I don't think these things need a separate thermostat. Unless you are away a long time, setbacks may not save you that much, and if used for moisture/humidity control, can be detrimental. Ideally, the thing would run 100% of the time, just meeting your needs while extracting the max amount of humidity. Short cycling is bad for that and overall efficiency.
  11. Dana

    Dana In the trades

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    What Jim-said- 20KBTU would be EXTREME overkill for a basement addition in a MD location.

    The 3/4 ton is probably somewhat overkill for heating a 360' addition (unless it's all glass walls with minimal ceiling insulation with huge wintertime losses and huge summertime solar gains), but it's as small as they get, and it'll be fine.

    Uninsulated a basement might have a heating load as high as 20K if it has a LOT of air leakage and 4' of exposed above grade foundation. With any wall insulation at all that drops to less than the heat load of your addition. The cooling load of most basements is essentially nil- it's all latent load (humidity.)

    You can probably mentally eyeball the basement for a really crude (but way better than a wag) I=B=R heat loss analysis even from Bagram. Assume that the heat loss through uninsulated CMU or poured concrete is about 1BTU per square foot of area per degree F, and only count the above grade portion of the house. Assume a 99% outside design temperature of about 15F, and assume that it's OK to let it drop to 65F for a few hours on the coldest night of the year (the 99% binned hourly condition).

    That's a delta-T of 50F, and a U-factor of 1BTU/square foot per degree, which means at design condition you're at 50BTU/ft of above-grade wall.

    Assuming a 25' x 40' basement and 2' of above-grade perimeter, that's 260 square feet. So the wall losses run about 50 x 260= 13,000 BTU/hr. If it's 3' of exposed above grade foundation you're hitting close to your 20K number, but you say it's mostly below grade.

    If you put up an inch of fire-rated iso up against the wall your U factor drops to about 0.14 BTU/sq-ft-degree-F, and the heat load is closer to 0.14 x 13,000= 1820BTU/hr. Yes, it's really THAT low, and the combined total of the below grade wall and slab might make it double that, and air leakage at the foundation sill & rim joist might add that much again, but it's still well within the output of a 3/4 ton mini-split.

    No matter what it's still worth air sealing the band joist and putting up rigid foam (fire rated iso needs no ignition barrier, but there are other cheaper/better methods if you're going to finish the walls) since that also reduces the amount of ground moisture & summertime air moisture that makes the basement more humid. I insulated my ~1500' basement (2' average above grade exposure) and rim-joist to R18 using reclaimed roofing iso, and it NEVER drops below 65F down there in winter, and a 70 pint room dehumidifier keeps it under 60% RH during the spring/summer/fall for well under 500kwh/year no matter how torrid it gets outside. (That would be less than $75/year at New England's electric rates, probably less for you.) It's been coasting along a 68-69F in the early part of the heating season, and may hit 65F during a sustained cold period, but without joist insulation on the first floor (except under the radiant zones) the basement typically runs 66-67F in mid-winter if we keep the first floor at 68-70F. If your boiler is cast iron and located in the basement you'll never need to explicitly heat the place during the heating season with insulated walls- the boiler losses to the basement will usually exceed the basement heat load during the coldest days.
  12. devans175

    devans175 New Member

    Messages:
    66
    Location:
    Maryland
    Thank You all for the detailed input! Dana, the addition does leak like a seive and there are some very large double pane windows. I've been working on the leaks. It's also build on an unconditioned crawl space which adds to the draftiness. Poor construction really, but I'll work it out and improve things as I make other improvements, and as you said, 3/4 ton is the minimum anyway.

    The basement, on the other hand is 99% below grade. The most that might be exposed is the rim joist. Before I finished the basement, I sealed and insulated the rim joist. I did a basic moisture test on the below grade walls and that didn't seem to be an issue. I agonized over whether or not to fully insulate the below grade walls after researching it and decided against it. It may have been the wrong decision, but it's too late now. I also replaced the small basement windows with some pretty good ones (they are below grade, in window wells). How does that affect the sizing of the basement unit? I followed the info you shared using the Load calcs, but I've never really been able to get a handle on the right way to factor in the uninsulated below grade portion. Your thoughts?

    Jim, I appreciate your input regarding the seperate thermostat. The humidity issue is important and I can see your point.
    Last edited: Nov 9, 2012
  13. Dana

    Dana In the trades

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    Insulating the walls still makes a difference in both the heat load and comfort levels, especially the top half. But unlike the above grade portion the heat loss doesn't track the hourly outside temperature due to the thermal mass and insulating effects of the soil. The heat loss roughly tracks the weekly or sometimes monthly average outdoor temp, but there are many variables (soil type and moisture levels, etc.), and the U-factor is also less than 1/3 that of exposed above grade foundation. From a financial point of view there is still a long-term return on putting R12-R15 on the foundation walls in your climate. See the table 2 p10 of this document, and read the first chapter.

    Maryland is in US climate zone 4, where they're recommending R15 for basement walls. To hit that in a way that won't create mold conditions in either winter or summer the portion of the wall stackup in contact with the wall must be foam, but the R-value can be fattened up with a batt-insulated non-structural studwall trapping the foam to the foundation. R4 of foam is sufficient to control wintertime condensation within a 2x4 studwall in your climate, which is cheaply done with 1" of unfaced EPS (compressed bead board- like cheap coolers, etc), at about 40 cents per square foot, sometimes less. Unfaced EPS is sufficiently permeable to water vapor that it still allows the foundation to dry toward the interior, which is important in some cases to keep the foundation sill from rotting, especially when there is minimal above grade exposure that would otherwise let the ground moisture dry to the exterior (which sounds like your case.) You could also use 3/4" or 1" XPS (pink, blue, green) but it's usually more expensive and has less drying capacity. Using foil faced iso may be risky when you have very little above grade drying capacity unless you have a metal or EPDM capillary break between the foundation sill and concrete. (That was my prior recommendation, but I'm pulling back on that since you're saying "99% below grade".)

    If you already finished it out with an uninsulated studwall butted up against the concrete you could still insulate it with non-expanding injection foam with relatively low mold risk. But just the gypsum and trapped air-films adds another R0.5 to the wall, reducing the U-factor a bit. Without some real insulation you'll still probably have to heat it to stay comfortable though.

    A cheap double-pane basement window has a U-factor of about 0.5-0.6, which is half that of an exposed concrete wall. A low-E version typically runs U0.32-0.36. But the total square footage is usually SO minimal that it hardly matters. Most 1000' basements would have less than 15 square feet of window, and at a delta-T of 50 F and U-factor of 0.5 that's (50 x 0.5 x 15= ) 225 BTU/hr of window losses. (A sleeping human emits more heat than that!) Even 65 watts of lighting (say, one 2-tube T8 fluorescent fixture) is enough to offset the window loss.

    Inverter drive mini-splits usually come with remote controls, and NOT a wall mounted thermostat. The interior air temp is sensed by the wall-cassette (and the incoming air when the blower is running.) Since they are fully modulating systems that run at highest efficiency at the low end of their blower & compressor speed, you're much better off with a "set and forget" strategy than using programmed setbacks, since it'll run at full blast (and lowest efficiency) on the recovery ramps, using more power than you saved. Turning them off (or way down) when you're going away for days still makes sense though.

    There are probably at least a dozen very good 3/4 ton mini-splits out there, and a handful of 2-head multi-splits under 20KBTU. I like Daikin Quaternity series for the ability to dehumidify in both heating & cooling modes, with programmable dehumidistat settings but they're not cheap. The 3/4 ton model is the RXG09HVJU using the FTXG09HVJU indoor cassette. It's rated for 12KBTU/hr max at 47F outdoor temp, but still puts out well over 9000BTU @ 17F under any outdoor humidity conditions (which affects defrost duty-cycle). It's cooling efficiency is 26 SEER, heating efficiency HSPF 11 (COP= 4.5@ 47F), which is way up there compared to bottom-end units.

    Others in that efficiency class (albeit with simpler-dumber dehumidify controls) are:

    Daikin RXS09LVJU/FTXG09HVJU rated 24 SEER/ 12.5 HSPF

    Fujitsu Halcyon 9RLFW/AOU9RLS2 , rated 26 SEER/12 HSPF

    Mitsubishi H2i series MSZFE-09NA / MUZFE-09NA rated 26 SEER/10 HSPF

    There are some good LGs and Sanyos and others of similar ratings, but the above three probably control a combined 90% of the US market (Mitsubishi is the biggest), so from a support point of view they're probably the best bets. IIRC under the hood many of the others use Fujitsu compressors and variable volume valving controls, etc, but with their own power, coils and control algorithms. Dehumidification mode is cooling only, and not under dehumidistat control the way the Daikin Quaternities are, but they're still pretty good.
  14. devans175

    devans175 New Member

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    Thanks Again Dana. I was considering the LGs because they described a feature called "Advanced INVERTER technology" which they claim provides energy efficient, variable output capacity. I found some info on the Daikins. It sounds like they do have some advantages over the others. The prices don't look extreme either. I read through all of what you gave me above and it's very informative, while a bit overwhelming. I had a hard time getting your final thoughts on the sizes. Were you saying a Dual Zone system with 2 - 9000 Btu heads would be appropriate? I wasn't able to find any info on the "quietness" either. LG claims 19 dbA. Are the Daikins in the same range? That's very quiet!!
  15. devans175

    devans175 New Member

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    I found some really good info on the sound levels of the systems you recomended.

    Daikin 37/25/22 dBA
    Fujitsu 40/36/31/26
    Mitsubishi 42/40/31/22
    LG 38/33/24

    The Daikin holds up with the others on sound, and has the ability to dehumidify in both heating & cooling modes, which the others don't. I think this is the best choice. Now all I need to do is determine what size need for the basement.
  16. Dana

    Dana In the trades

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    The any 9000BTU (cooling mode rating) mini-split heat put would heat & cool your basement, and would be able deliver something like 11-12000BTU/hr at full compressor & blower speed at your outside design temp.

    On the noise levels, note that most refrigerators that put out noise higher than 40dbA. I set up my mother's place (western WA, design temp of ~20F) to heat her whole house with a 1.5 ton Mitsubishi (good for output of ~21KBTU/hr in heating mode down to about +5F, falling to~15kbtu/hr @ -13F). It's louder than her refrigerator only at the highest blower speed, but she programmed it for low-speed only, even though that limits the maximum heat output. She may kick it up during a cold snap, but she hasn't had to do it yet. (It was installed in late February this year, IIRC.) Odds are pretty good that your basement mini-split would never have to come off the lowest blower speed, but may modulate a bit in compressor speed.

    Any of the models I suggested are inverter drive with fully variable compressor & blower speeds, as are the better LGs. Some cheaper interior cassettes/heads are 2-speed AC motors and not quite as efficient or quiet, but they're still not bad. Any mini-split with an HSPF rating better than 8.5 will have a fully variable speed inverter drive compressor though, even if they might use cheaper blower motors & controls on the cassette.

    SFAIK Daikin doesn't make a 2-head Quaternity to take advantage of the more sophisticated dehumidification mode. If that's a compelling feature for you it may mean buying two separate units. If the basement and the addition are close to one another it may make sense to do one of those. If separated by a longer distance than 10meters/35 feet from where you set up the outside unit you can run into issues with maximum lengths on the refrigeration lines and control cables, which would drive you toward two complete units.

    An off-the top of my head, a short list of pretty-good ~1.5 ton dual heads are

    Mitsubishi MXZ-2B20NA

    Fujistu AOU18RLXFZ

    Daikin 2MXS18GVJU

    These all run ~18 SEER, and in the low-9s for HSPF.

    With most 1.5 ton duals it's easy to mix 'n match heads: 9K + 9K, 7K+12K, 7K+9K, or 7K+ 7K (derating total output down to 14KBTU/hr which might be right for your situation unless you anticipate a bigger cooling load than 7KBTU/hr for the addition, which may be the case.) The hardware cost for the outdoor unit would run ~$2.5-3K, then about $350-500/head (x2), plus installation, so it would likely hit $5-6K, installed.

    A pair of 3/4 ton LGs like the LS090HYV may cost only slightly more (or maybe even less than a dual head Daikin), and comes with more favorable efficiency numbers (SEER28/HSPF12), but it's hard to say. With most of these the cassettes are powered by the outdoor units, which limits the amount of AC wiring necessary for installation. Some installation issues double when you install two outdoor units, but it can sometimes be simpler to go with two.

    It's a moving target and a competitive market, since small mini-splits hold a lion's share of the Asian space heating. You can even buy a Chigo in the US, if you thing you will be feeling nostalgic about Afghanistan, but SFAIK they don't have any super-efficient models yet like the big Japanese & Korean manufacturers do. The US is a late-comer to the technology, and with larger more sprawling & doored-off houses ducted systems are still the paradigm, but as awareness grows, so does the mini-split market.
  17. devans175

    devans175 New Member

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    Location:
    Maryland
    Oh.. I see. Daikin doesn't offer a multi zone Quaternity. I wonder if they're working on that. I was wondering why your previous post recomended the single zone with the 9000 BTU head. I'd actually prefer a two zone. The addition and the basement location are close to each other. I'll crunch the numbers and see what makes more sense... Thanks!!!!
  18. Dana

    Dana In the trades

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    I too wish Daikin made a multi-zone Quaternity- the bit of cleverness that allows dehumidification control in either heating or cooling modes is almost entirely in the interior head (a special split coil and valving system), but there may be compatibility issues with the control & communication with the outdoor half of the system that makes it awkward when two zones are calling for conflicting compressor speeds due to differing dehumidifcation modes(?). It's true that no multi- can run one head in heating mode and the other in cooling mode at the same time, but IIRC you can run one in cooling and the other in (not-so clever) dehumidification mode, since the dumb-dehumidification is basically a cooling mode with the blower running very slow to minimize the coil temp to just above frost levels, maximizing condensation.
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