Page 2 of 2 FirstFirst 12
Results 14 to 22 of 22
  1. #14
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    6,868
    Post Likes
    Quote Originally Posted by Poodle Head Mikey View Post
    I picture that it takes less work, and has less operating cost, to run a 5 ton system where a 2 ton system would be the proper size. To the same indoor temperature. Especially once the heat-soak of the structure is gone. And I imagine this might be a decent way to go about things in places where the outdoor humidity is always low.

    But back to what I started out with - IF a two-stage system had BOTH of the stages optimized for dehumidification - then I think the advantages would outweigh the costs.

    My question is: Are They Ever set up that way? Or are they even capable of being set up that way? And I mean with the cooling coil always 30 below the RAT? In both stages?

    I do not know, but I picture that low-stage operation is just left to 'run wild', so the evap. temperature trends high and so the best advantages of the smaller capacity are never realized. Is that accurate?

    PHM
    ------------
    Yea, if set up properly most all the 2stage systems slow down the indoor fan to match the cooling capacity on first stage.


    Sent from my iPhone using Tapatalk

  2. #15
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    6,868
    Post Likes
    Quote Originally Posted by ats1986 View Post
    Is that true though? I have to think that your house is gaining more BTUs per hour if you keep it at 75 than if it is at 85. Which means those extra BTUs are having to be removed as they are gained. If your house can just get up to 85 or whatever it will maintain with out a/c throughout the day then you will no have to remove several hours worth of heat gain.

    Again, I have almost zero real training on this topic so I could be totally wrong.


    Your not totally wrong, the amount of heat transfer is based on the heat difference but, The difference is probably negligible.

    What I didnt think of last night is say you have a 5ton 2stage in a 2.5ton home. The 5t will actually be doing less work to quickly pull the house down because its actually doing less to get the sensible temperature to desired set point. I.E its not getting the moisture out of the air so less total enthalpy is actually removed.


    Sent from my iPhone using Tapatalk

  3. #16
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    24,694
    Post Likes
    For what it is worth, it does take less energy to pull a hot house down late in the day, than it does to run the A/C all day. And exactly for the reason you stated in your first sentence here. Wanted to comment on your prior post on the topic in this thread, just been waiting for the time.

    If the TD of the outside air versus the inside air decreases at some point, then that would be the beginning of your savings. On a bit of a tangent, here's an interesting scenario that happened several years back in California, where I live. It was a hot spell. So the electric company (PG&E) told everyone to leave their AC's off until they got home from work.

    Well shiver my timbers, there was such a huge demand for electricity late in the day, it almost shut the system down state wide. So they came out with a revised recommendation. Set your stat at 78*F during the day, then lower it when you get home. That way it did not overload the electrical grid at 5-6 PM.

    Personally, in the summer, with no one in the house, I leave my stat at 81*F. When I get home, I crank it down to 70*F and it usually doesn't shut off. I mean, if it is at 81*F when I get home. Works for me. Pisses me off when it turns off; being in this trade has made me acutely aware of temps and humidities. I just love having that cold low humidity air falling on me.

    Problem is, at least where I live, if the system is put in per code, you cannot oversize the system. Which mine isn't. Just saying, you gonna have to do it on the sly.

    I personally would have no problem with a perfectly designed system that was super efficient and would run continuous at design and meet every ridiculous code that was out there. Then have a secondary system in series with the primary that would kick in for hot pull downs.

    All that said, improvements to the structure can go a LONG LONG ways. My house was built in 1958 with no insulation. Previous owner had some of that cellulose insulation blown in, so at least there's something besides just air in the walls now.

    After being here for several years, the slider to the patio cracked, so I had to replace that. What a freakin' difference!

    And just 'one' piece of glass.

    If I were to yank all of the single pain encasement windows and replace with high efficiency windows, there would be a pay back. But I just haven't found the motivation. Point being, keep the heat transfer down, that's where you can really save some long term monies.


    Quote Originally Posted by Core_d View Post
    Your not totally wrong, the amount of heat transfer is based on the heat difference but, The difference is probably negligible.

    What I didnt think of last night is say you have a 5ton 2stage in a 2.5ton home. The 5t will actually be doing less work to quickly pull the house down because its actually doing less to get the sensible temperature to desired set point. I.E its not getting the moisture out of the air so less total enthalpy is actually removed.


    Sent from my iPhone using Tapatalk
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  4. #17
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    6,868
    Post Likes
    Quote Originally Posted by BBeerme View Post
    For what it is worth, it does take less energy to pull a hot house down late in the day, than it does to run the A/C all day. And exactly for the reason you stated in your first sentence here. Wanted to comment on your prior post on the topic in this thread, just been waiting for the time.

    If the TD of the outside air versus the inside air decreases at some point, then that would be the beginning of your savings. On a bit of a tangent, here's an interesting scenario that happened several years back in California, where I live. It was a hot spell. So the electric company (PG&E) told everyone to leave their AC's off until they got home from work.

    Well shiver my timbers, there was such a huge demand for electricity late in the day, it almost shut the system down state wide. So they came out with a revised recommendation. Set your stat at 78*F during the day, then lower it when you get home. That way it did not overload the electrical grid at 5-6 PM.

    Personally, in the summer, with no one in the house, I leave my stat at 81*F. When I get home, I crank it down to 70*F and it usually doesn't shut off. I mean, if it is at 81*F when I get home. Works for me. Pisses me off when it turns off; being in this trade has made me acutely aware of temps and humidities. I just love having that cold low humidity air falling on me.

    Problem is, at least where I live, if the system is put in per code, you cannot oversize the system. Which mine isn't. Just saying, you gonna have to do it on the sly.

    I personally would have no problem with a perfectly designed system that was super efficient and would run continuous at design and meet every ridiculous code that was out there. Then have a secondary system in series with the primary that would kick in for hot pull downs.

    All that said, improvements to the structure can go a LONG LONG ways. My house was built in 1958 with no insulation. Previous owner had some of that cellulose insulation blown in, so at least there's something besides just air in the walls now.

    After being here for several years, the slider to the patio cracked, so I had to replace that. What a freakin' difference!

    And just 'one' piece of glass.

    If I were to yank all of the single pain encasement windows and replace with high efficiency windows, there would be a pay back. But I just haven't found the motivation. Point being, keep the heat transfer down, that's where you can really save some long term monies.
    Yeah but your system is more-less properly sized. I dont think youd be as comfortable if you banged on a way oversized system when you got home and the saving you would reap if any would be pennies per the ton.


    Sent from my iPhone using Tapatalk

  5. #18
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    24,694
    Post Likes
    If I had the choice, I'd throw on a hot gas valve on that oversized system.

    I'd be so comfortable. The compressor could run at max. And it could run with almost no load and not freeze.

    The real question in this thread is two fold. Efficiency or immediate comfort.

    Each of us needs to decide what we want. And what we want to pay for.


    Quote Originally Posted by Core_d View Post
    Yeah but your system is more-less properly sized. I dont think youd be as comfortable if you banged on a way oversized system when you got home and the saving you would reap if any would be pennies per the ton.


    Sent from my iPhone using Tapatalk
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  6. #19
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    6,868
    Post Likes
    Quote Originally Posted by BBeerme View Post
    If I had the choice, I'd throw on a hot gas valve on that oversized system.

    I'd be so comfortable. The compressor could run at max. And it could run with almost no load and not freeze.

    The real question in this thread is two fold. Efficiency or immediate comfort.

    Each of us needs to decide what we want. And what we want to pay for.




    Sent from my iPhone using Tapatalk

  7. #20
    Join Date
    Jun 2019
    Posts
    11
    Post Likes
    The best pick is always to go with the variable speed motor air conditioning unit. It uses a good amount of power initially as compared to the fixed speed motor allowing your room to cool down faster. Also, a variable speed motor will adjust the compressor workload as per thermostats requirement.
    However, a larger unit can cool better but what is the point here. We are talking efficiency here that simply means a regular unit will be fine.

  8. #21
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    41,894
    Post Likes
    We install a lot of 2 stage units, and some inverters... note that inverter split systems (conventional design equipment) should NOT be put on a house unless the furnace/coil is centrally located and the duct runs are short... as air will not get out to the far ends of the duct runs most of the time. And you will have an un-happy customer!

    With the 2 stage units:
    Design temp in Atlanta is 92*F... however that can be anywhere from 60-90% RH... (ooops)...
    So the load is not really constant.

    AND... I can tell you this from experience: If we have a HOT summer (days in the mid 90's or upper 90's)... and the system runs full time and cannot get the house cooled down until after dark...
    YOU are gonna get lots of BAD reviews!
    Customers do NOT care about what the ACCA says... they want to be comfortable... which means they want to FEEL comfortable... and it is YOUR job to deliver that!

    Herein, lies the advantage of a 2 stage unit:
    Lets say we did a Load Calc on the house... and it says right at 3 tons (lets say 35K BTU's total load, because we know most 3T units do not actually do 36K BTU's).
    SOOO... a 4T 2-stage unit will almost make design most of the time in low stage (remember, a 2 stage unit is about 70% in low, which is about 33,500 BTU's.
    So we have the low stage running most of the time, it is about 1500 BTU's under-sized... which is great for longer run times and good de-humidification (we have humid summers).
    Now look at those HOT days... which are above design temp... the unit can go to high (always use a 2 stage stat)... and cover the load!
    And as noted in a previous post: Say the customer has a party on a summer day, with 20 guests and cooking... the added capacity will go a LONG ways to holding temp... where the barely capable single stage will just loose ground!

    Now one needs to remember: Match the equipment properly:
    4T 2-stage outdoor unit
    Matching 4T VS furnace
    Proper coil with proper TXV valve
    Large enough media filter
    Added return so the system can suck 1600 CFM's of air when asked to do so...
    Yeah, the supply will be a bit low for the full CFM's... however the system will not run there much and that is what a VS motor does well!
    We have dozens and dozens... probably over a hundred... installs of systems similar to this... and ZERO VS blower issues!

    And of course, a quality stat (we like to use the factory communicating stats, or high end Honeywells).

    We install anywhere from half a dozen to over a dozen of these high end systems a season... and we have literally NEVER had a customer complain about how comfortable their home feels...
    NEVER!

    We do, however, get a lot of referrals from these jobs...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

  9. #22
    Join Date
    Mar 2019
    Posts
    13
    Post Likes
    Are you a technican? or why are you interested in knowledge of energy effiicency and usage.
    usually the calculations and the best use come from experience. once you will fix the systems, you will become expert in knowledge.

Page 2 of 2 FirstFirst 12

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •