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  1. #14
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    The heat pump is likely to kick the crap out of any 20 year old boiler from cost effective perspective. Financial balance point is probably below zero. Did he run opcost for you?

    Locking out at 35 for any logical reason, or legacy bias on the installers part? Maybe he's stuck thinking all heat pumps are the same as ones he installed in the 80's. Your equipment is like comparing a current notebook computer with a typewriter.

    Disable the lockout. Find out how low it can go before register temps start getting cool. Then decide if you want to lockout somewhere above that.

    Did you install a humidifier? Media filter? If so, you'll get significantly more comfort running the pump.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  2. #15
    Join Date
    Apr 2012
    Posts
    60
    Quote Originally Posted by tedkidd View Post
    The heat pump is likely to kick the crap out of any 20 year old boiler from cost effective perspective. Financial balance point is probably below zero. Did he run opcost for you?

    Locking out at 35 for any logical reason, or legacy bias on the installers part? Maybe he's stuck thinking all heat pumps are the same as ones he installed in the 80's. Your equipment is like comparing a current notebook computer with a typewriter.

    Disable the lockout. Find out how low it can go before register temps start getting cool. Then decide if you want to lockout somewhere above that.

    Did you install a humidifier? Media filter? If so, you'll get significantly more comfort running the pump.
    The installers weren't that interested in an HP at all, I kind of had to talk them into it. So their advice has been minimal, I have tried to figure it out.
    BTW: Got an Aprilaire 13MERV, no humidifier (might be an interesting idea, but haven't been using one).

    Uou have motivated me to spend some time checking out the statistics:
    from http://www.docs.hvacpartners.com/idc...25hnb9-3pd.pdf (just the heating...)

    AHRI , compressor , fancoil , high temp (47df) capacity and cop, hpsf, low temp (17df) capacity and cop

    5227002 , 25HNB924A**30 , FE4ANF002+UI , 25,600 4.16 , 9.7 , 15,200 2.88

    Note that interpolating gives:
    ( temp cop): 47 4.16 , 42 2.94 , 35 3.6 , 27 3.3 , 22 3.1, 17 3.0

    Now ..
    Electricity is $0.15/kwh
    NG is $1.10/therm; at 29.3 kwh /therm : 1.10/29.3 = $0.037/kwh
    Say my boiler has an efficiency of ~ 66%: 0.037/0.66 - $0.0568/delivered kwh

    So, break even ratio for using hp: 0.15 / 0.0568 = 2.67

    If the boiler is more efficient (say, 75%) breakeven would be 3.04

    It appears I should reevaluate (perhaps start with a cutout of 15d) .... I show how had a notion of COP=3.0 at 35d, and lower NG prices.

    So thanks for alerting me!

    BTW: that doesn't change the original subject of this thread: using the boiler during power outages (when I can use a 6.5kw genset to
    run a portion of the house, including boiler water pump, etc BUT NOT the hpac)

  3. #16
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    I have a similar, if somewhat more complicated system in my own home, installed by yours truly. My system is a multi-zone hydronic system combined with a 3-zone Bryant 2-stage Evolution (same as Carrier Infinity) HP. So here's the operational deal.

    The confusion enters when you try to use the hydronic system for aux heat, such as defrost of supplemental in cold weather. The problem is, the only thing the Infinity User Interface will control is the air handler and HP. When it wants aux heat, it will, with the proper wiring harness installed, call on the boiler but it will also turn on the air handler. So...what to do?

    The first thing is to recognize the limitations of the system. Thus, the hydro-air harness is installed but is connected to nothing. The sole purpose of the hydro-air harness is to give feedback to the User Interface that there's a hydronic application present. That, in turn, is what alters the User Interface such that it will allow the set-up to include a HP "lock out" temperature, which is that temperature below which the HP will not be called on. So, if set for 32F, any outdoor temp below 32 will not allow the HP to run. Thus, both the HP and the air handler are 'stopped', unless you've got 'continuous' fan selected, at which point the indoor fan will blow at the selected comfort level. Now how to get the heat on below 32F. That's where a conventional heating thermostat comes into play. I have two t-stats right beside each other, one for the HP and one for the boiler. I set the boiler temp just 1 below the HP so the transition from HP to hydronic is seamless and unnoticed. Once the HP is locked out, the room temp falls 1F before the digital hydronic t-stat senses the low temp and begins to maintain room setting 1F below the HP setting. When the weather improves to 32F or above, the UI senses the low room temperature and raises it 1F above the hydronic setting so the boiler turns off and the HP takes over. Other than having 2 stats next to each other in each zone, it works like a charm.

    I did the system back when I had oil heat and wanted to beat the large heating bills. The HP use varies according to outdoor weather so a cold winter doesn't give as much benefit as a warm winter but the 2-years I used oil, it did cut oil consumption between 30% and 40% each year.

    As far as the generator is concerned, if you just use the arrangement I've given you, you don't have to worry about the HP being unpowered when you're on generator. But if you're determined to use the UI as the source of control, it gets it's electrical power from the air handler and the air handler should be on its own electrical circuit at the main electrical panel. Your electrician should be able to route that circuit (variable speed blower, very low amps) through the gentran switch gear so the air handler/UI get power. Mind you though, the UI is VERY sensitive to frequency and power fluctuations. You could encounter all manner of malfunctions or error codes on generator power, unless it's 100% on frequency and voltage at all times.
    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!

  4. #17
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    Good for you for driving that purchase! I think you'll be very happy with that decision. Definitely get a humidifier. It's something that may run very seldom, but will matter. I like this humidifier:

    http://www.docs.hvacpartners.com/idc...-humwbp-01.pdf

    Don't get hung up on COP, gas efficiency, etc. The times that heat pump costs more to run than your boiler are so rare in your neck of the woods doesn't merit the time to do the calculations. I bet they'd come back at $10 a year, which would be impossible to verify with M&V. IMO, amounts to small to verify aren't worth chasing. Sometimes unverifiable "savings" actually end up costing money.

    My approach would be the one Beenthere suggested, separate tstat for boiler. Also, turn the boiler OFF and determine how much load the HP can carry before register temps bother you.

    Installer accidentally locked out natural gas on my mother's unit. She called me on a 7f night asking if cold air at registers indicated a problem, prefacing the conversation with "it's 70f in here and very comfortable but..."

    It's really nice to understand where that point is for your house. Tells you about the homes ACTUAL load.


    Skip has huge infinity knowledge, might browse his threads. Their fun to read and you'll glean a lot from them.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  5. #18
    Join Date
    Apr 2012
    Posts
    60
    Quote Originally Posted by tedkidd View Post
    Good for you for driving that purchase! I think you'll be very happy with that decision. Definitely get a humidifier. It's something that may run very seldom, but will matter. I like this humidifier:

    http://www.docs.hvacpartners.com/idc...-humwbp-01.pdf

    Don't get hung up on COP, gas efficiency, etc. The times that heat pump costs more to run than your boiler are so rare in your neck of the woods doesn't merit the time to do the calculations. I bet they'd come back at $10 a year, which would be impossible to verify with M&V. IMO, amounts to small to verify aren't worth chasing. Sometimes unverifiable "savings" actually end up costing money.

    My approach would be the one Beenthere suggested, separate tstat for boiler. Also, turn the boiler OFF and determine how much load the HP can carry before register temps bother you.

    Installer accidentally locked out natural gas on my mother's unit. She called me on a 7f night asking if cold air at registers indicated a problem, prefacing the conversation with "it's 70f in here and very comfortable but..."

    It's really nice to understand where that point is for your house. Tells you about the homes ACTUAL load.


    Skip has huge infinity knowledge, might browse his threads. Their fun to read and you'll glean a lot from them.
    It does get dry in the house in the winter (my skin notices it). But the boiler is in the cellar, and the hvac duct work is in the attic, no water up there (the AC was a retrofit when we moved in)!
    Running a water pipe up there probably makes it to expen$ive. Or is there some clever trick?

    Will see when winter comes how it works. One issue is the ducts are a bit noisy (that is a whole other story); and I kind of am used to the baseboard. How well will I like the
    ceiling mounted ducts delivering hot air? I will definitely have to experiment once heating season arrives (I have no problem tweaking the Infinity advanced settings).
    Not sure what advantage is there to shutting off the boiler altogether -- if it isn't running does it really consume any kind of power?

    BTW: skip helped me before, convinced me that it is possible for the existing boiler and the new Infinity to play together. So his post (hi Skip!) was old news for me.

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