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  1. #1
    Join Date
    Apr 2002
    Location
    Houston
    Posts
    25
    I want to replacing both (old mercury type) thermostats in my house with Visionpro or similar programmable stats. The house has a large atrium connecting the upstairs/downstairs, so I want to have a programmable fan or circulation feature to try and prevent u.s./d.s. temperatures from getting too far out of balance during times when the a/c or heat isn't running much. Would rather not run the fan 100% of the time though.

    I read in another post that the VisionPro has a circulation feature, but that it isn't smart enough (when circulation mode is selected) to prevent the fan from running for the few minutes immediately after the A/C shuts off.... and that by allowing the fan to continue running after a cooling cycle, humidity removal suffers.

    Can anyone confirm if this "flaw" is has been corrected in the VisionPro thermostats??

    Is it a significant drawback for Humidity control (I live in Houston)?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,302
    You can tell the Vision Pro no fan on after cool cycle. The "circ" setting is random, 20 minutes an hour I believe. Not sure if it will start that 20 minutes right after a cool or not. Running the blower more than a minute after cooling shuts down does cause re-evaporation of the condensate. Mostly a problem in mild, damp weather, not in hot weather when the unit is running most of the time.

  3. #3
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    VisionPro design

    I telephoned Honeywell a couple months ago and persisted until they told me they *don't* restart the off-period at the end of a cooling cycle, they just allow random fan running any old time. You are exactly right that this could simply be solved by a tiny software change. I would *love* to hear if and when they do this. However the company seemed arrogant, they had difficulty even comprehending the problem, and replied to me that I had "special needs" or some such. Yeah, me and maybe 30 million other people in hot-humid climates. Damn Minnesotans <g>.

    What Baldloonie said, I agree with totally. However one of his phrases...
    >>Mostly a problem in mild, damp weather, not in hot weather when the unit is running most of the time.

    I have to reply that the 35% random fan runtime feature of the VisionPro, is completely irrelevant if the A/C runs more than 35% of the time. By its very nature, that feature is for periods when neither A/C nor heating is running much.

    All other aspects of the VisionPro look great -- the only thermostat that makes me want to buy it because of its looks. If you take care, you might be able to use it OK in your application. If you try it, you can buy a couple humidity meters ($15 at Wal-Mart) and just observe whether a humidity problem exists for you.

    Best of luck -- P.Student

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,302
    I'm saying that running the fan constantly and putting moisture back in the air is more of a problem in cooler, damp weather when the unit is contantly cycling than in hot weather when it is running most of the time.

    So Honeywell said that the fan circ feature is a totally random time? So then it's possible that it is immediately after a cool cycle but odds are slim and it would be pretty rare, not worth worrying about to me.

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    If humidity is an issue and you want to go with the VisionPro, I'd look into the 8321 model, with humidistat. Essentially the humidistat is an overcool feature, in that it allows the cooling cycle to run a few degrees below setpoint in order to accomplish dehumidification. It will not allow the system to continue running if dehumidification has not been met but the temperature has gone below setpoing as far as allowed. In other words it will not override setpoint and just keep cooling until the humidistat is satisfied, which could be never on a high humidity day with constant door opening and closing going on in the house.

    To me the proper overall approach to humdity control in a muggy climate is a tight house kept at a positive pressure with decent insulation, with an ERV to maintain fresh air without upsetting humidity levels. Add to this a form of modulation or capacity control for the HVAC system to deal with days where humidity levels are high but sensible heat loads are lower and you have a system that will perform well under a wide variety of conditions.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Perspective

    I didn't quite understand your earlier message the way you meant it, thanks for clarifying. I am highly interested in what conditions make this shortcoming into the "unimportant" category. Certainly it is 2/3 less of a problem than running the fan constantly, I will remember your professional opinion. Thanks.

    I am wary of this product in Houston, but really look forward to somebody else taking the risk and telling me how it works. You could look at it this way -- try the Visionpro, take some measurements, and if humidity is impaired by the random-fan feature then disable it and connect an AirCycler to the circuit. A plus would be the AirCycler could choose a different duty cycle than 35%, and it knows enough not to be random.

    I have personal experience with the Houston climate. There is only a short time interval when the weather is mild and humid, *and* the A/C runs. When the heat is on, it won't be a problem. When the A/C gets to seriously running, it won't be a problem. Because Houston has a long hot summer and brief periods of spring and fall (and winter barely exists), this might not be such a bad idea after all.

    Best wishes -- P.Student

    P.S. I read Shophound's idea and I must point out ERVs are practically unheard of in this region. Not saying that's the way it should be... rhetorically, are we ignorant rubes or do we know something the other guys in the country don't? In the interests of what's more familiar I would prefer to endorse Teddy Bear's concept of a ventilating dehumidifier in its place. Not exactly the same function but I believe it's what we need in the Houston area (I am in Fulshear about 30 miles west).

    [Edited by perpetual_student on 03-16-2005 at 12:56 PM]

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    P.S. I read Shophound's idea and I must point out ERVs are practically unheard of in this region. Not saying that's the way it should be... rhetorically, are we ignorant rubes or do we know something the other guys in the country don't? In the interests of what's more familiar I would prefer to endorse Teddy Bear's concept of a ventilating dehumidifier in its place. Not exactly the same function but I believe it's what we need in the Houston area (I am in Fulshear about 30 miles west).
    If you listen to David Debian of Central City Air in Houston, it would appear that few HVAC companies in the Houston area know how to properly deal with their humid climate. I don't think he's off the mark. Last week I attended a heat pump seminar and RSES conference in Ft. Worth, and spoke with other techs and contractors in the field. The overall consensus would indicate that it's possible up to 80% of residential HVAC service technicians in the DFW area are not adequately trained to do the work.

    If you take that as fact, what are your chances of you getting someone into your home that REALLY understands proper humidity control, particularly in tight construction (where an ERV would be beneficial due to the necessity to exchange the air without sacrificing humidity control)? Not great.

    Another aggravating factor is that so many homes going up these days are built with about as much care as the training invested in many of the residential techs. I hear lots of talk about "tight construction" but when I walk through some of these new houses going up, I'm shaking my head and wondering, "What tight construction? This thing has more holes than Swiss cheese!"
    Add to that the quality of the average new construction HVAC system install and, well, there you are.

    PS, check out this website for details on ERV's and HRV's. I'm not a rep for this company but I found the info there interesting:

    http://www.fantech.net/hrv_erv.htm

    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    In my experience only a slim minority of HVAC installers respect humidity as one of their success criteria. Debien is one of them, wish there were more. But since most homeowners don't ever look at their RH (Relative Humidity), what can you expect? I kinda wish HVAC guys would hand out humidity meters at cost, and wish they would sell filters at cost since so many complain bitterly about what the homeowner buys. But that is wishing and may not be so wise if I thought about all the angles.

    Since we are looking at interesting ERV websites, let me add one which is technically very interesting:
    http://www.ultimateair.com/store/recoupaerators.html

    They claim to be the most efficient. It's easy to be a fan of efficiency. However when I get down to earth and try to decide where to spend my money, I'm not at all sure it would be a good investment in a hot-humid climate.

    Whereas I am sure that this product would yield benefits my whole family could feel:
    http://www.thermastor.com/100v.htm
    As an aside, I am skeptical about their sqft recommendations. Seems to me that is no more legitimate than sizing AC by tons/sqft. But it would take a lot of science and math to come up with a different number.

    Hope this helps -- P.Student

  9. #9
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    P. Student...

    We may be looking at apples and oranges here. It depends on where the emphasis is to be for dehumification. The HVAC system or a separate dehumdifier that discharges into the supply side of the HVAC ductwork downstream of the HVAC evap coil.

    If the HVAC is to be the primary dehumdification source, then IMO an ERV in tightly constructed homes makes sense as it will temper outside make-up air going into the air handler to lower the latent load on the evaporator, while ensuring an adequate fresh air exchange in accordance with ASHRAE standards.

    The separate dehumidifier you're looking at will also accomplish air exchanges but will also incur the extra energy necessary to run it apart from the A/C system (as will an ERV, but less so because it doesn't use a compressor).

    Since Houston's humidity is more often than not accompanied by high temperatures (I have family in Houston and visit fairly often), seems to me the better way to go is to design the HVAC system to accomplish good humidity removal, and if air exchange is critical, then an ERV will fit the bill for that purpose.
    If I lived in a climate where temperatures were moderate but the climate was humid, I'd look at the whole house dehumidifier.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  10. #10
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453
    Boy, all I can say is that you guys must work for some rich people who can afford erv's, hrv's, etc.
    Not only is the installations quite expensive, but you also have to worry about repairs. Its amazing that we have all lived for so long when we didn't have this 'stuff'.

    Now don't get me wrong, I think that there is a place for hrv's and erv's, etc, but not in everyones home.
    I can't imagine a situation where my indoor air quality would be so bad that normal door / window openings and infiltration won't exchange the air in my home enough ( with filters in my system ) to keep my air decently clean.
    ( and i smoke ).

    Have been to many residencies that had humidifiers installed when the system was new, but were not working when I had to repair the system. And guess what, the HO didn't even know it wasn't working. So how much of a true difference can these things make - in a usual situation ?

    I have never had a HO to call to repair his/her humidifier or de-humidifier.
    And we have very hot,humid climate

    So to me, these things may make a slightly better system, but not enough to cover the costs involved, and most people wouldn't know if these things were working or not.

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Born,

    That's what's good about this site. I'm just beginning to study more deeply the field of IAQ and what might be involved. Feedback like yours is helpful in that it's based on real world conditions, not pie-in-the-sky idealism (which is where a lot of mindset is in the design phase of things).

    What I keep hearing (often used as a sales pitch) is that in tightly constructed homes, indoor air pollution may be worse than outdoor air pollution, due to a lack of air exchange otherwise accomplished via infiltration in more loosely built structures. Hence, the introduction of HRV's and ERV's to provide the ventilation necessary to tight construction.

    What you're saying is that even in tight homes, door openings and etc. may be adequate to address recommended air exchanges?

    I still lean toward the HVAC system being designed, sized, and installed correctly for its climate. For humid climates I wouldn't go with anything less than a TXV on a single speed, single stage system. It provides far better capacity control and latent heat removal performance than a piston any day.

    I would also have to agree there seems to be an aspect of diminishing return on investment for systems much over 13 SEER. The 19 SEER systems with modulating compressors, ERV's, and variable speed blowers sound wonderful and I say if the resident wants that precise level of home comfort, more power to him, especially if comfort is his emphasis over energy savings ROI.

    Given the prior discussion on this thread, if the majority of existing systems 13 SEER and below were far better installed and maintained than they are, the level of satisfaction from the public toward our industry would be a lot higher.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Join Date
    Jan 2005
    Posts
    340
    Originally posted by BaldLoonie
    So Honeywell said that the fan circ feature is a totally random time?
    The circulate feature is explained in the home owners manual (document 69-1701). When the fan is set to circ, the thermostat will energize the fan for approximately 35% of the time. If the equipment runs for 20% of that hour, the fan will run for approximately an additional 15% of the time. I don't know how 'smart' the timing algorithm is.

  13. #13
    Join Date
    Apr 2002
    Location
    Houston
    Posts
    25
    BaldLoonie, P. Student, shophound, bornriding, travisfl - much thanks. Learned a lot more than I bargained for just "listening" to you guys kick ideas around.

    P. Student - I've got a humidity meter that I "watch" pretty frequently. The system is already giving me what I think is decent humidity control (by design, or by chance)... with fan on auto, tends to stay between 40 & 52-53%, very rarely higher. If I go with the VisionPro, I'll try the circulation mode and watch the humidity for a while and "report" back and let you know if it's the same, or noticeably worse. Won't be very scientific, but at least it's one data point.

    THANKS AGAIN ALL.

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