Spin?
Unless you live in the sticks, KWh meters are rapidly going digital. ;-)
-- -john wide-open at throttle dot info
~~~~~~~~ "The first step in intelligent tinkering is to save all the parts." - Aldo Leopold ~~~~~~~~
Rapidly doesn't mean completely
In sci.physics, Robert Morein
wrote on Sat, 31 Jul 2004 14:32:50 -0700 :
I would be surprised if meters are replaced just because the readers want digital. Most likely the meters are replaced when the building is rewired, and that's fairly rare. New buildings, of course, will get the new meters.
I see the same problem here as with highway signs: how many metric highway signs have you seen lately? :-) Probably not many. I'm not sure if new highway signs are even required to be metric -- certainly the roadwork projects here aren't using km yet.
In any event, kWh already *is* generally metric, although one might make a (weak) case that they should be reading either joules, kilojoules, or megajoules. (1 kWh = 3.6 MJ. The nearest Imperial unit might be a BTU.)
About 88 average over 24 hours, and about 82 at night...
Newton said the rate of heatflow into a building is proportional to the indoor-outdoor temperature difference. IMO, turning the AC off will save energy, even if only for a few minutes.
This wouldn't help, with a constant COP that doesn't fall with a higher indoor-outdoor temp diff. But it might, if the AC can move more heat energy with the same electrical energy at night, given a smaller night temp diff, eg if the COP were 3.3 at night and 3.0 during the day, or with lower off-peak electric rates.
A 4" floorslab can store about 8 Btu/F-ft^2 with a 4-hour time constant. It might cool from 75 to 70+(75-70)e^(-16/4) = 70.1 F after 16 hours in 70 F air. With R20 insulation outside, RC = 20F-h/Btux8Btu/F = 160 hours, so it might only warm from 70.1 to 94+(70.1-94)e^(-8/160) = 71.3 in 8 hours when it's 94 F outdoors. Or less, with little air movement in the house. A slab or a basement might be a efficient place to store coolth during a daytime setback, since cool air falls. We might only bring coolth up into the living space with a ceiling fan and a thermostat and an occupancy sensor as needed.
That would say it's a small difference.
I imagine so. How much less? How does the COP depend on the temp diff?
Definitely. But I'd use rainwater, with no minerals.
Shading should help, but as others say, the improvement may be small.
Maybe not, if you are seated :-) You might look up "displacement ventilation."
Why on earth would you say that? Do you work for Turtle Power and Light? :-)
I wonder what goes wrong. It can't keep up with the cooling load? At any rate, just putting the fridge inside a house with some thermal mass and shaded windows and little internal heat gain may be enough. Very few places in the US have a 24-hour daily average temp over 95, and fewer still have average night temps above 95. A house on vacation might keep itself cool with night air, using an exhaust fan and a differential thermostat that turns the fan off when outdoor air is a few degrees warmer than indoor air (to account for internal heat gain.) Brand Electronics may soon be selling a controller like this.
In wintertime, I unplug the barn fridge and keep the apples and carrots from freezing with a 100 W bulb in a trouble light in a lower bin, using an EH38 "Easy Heat thermostatically controlled device" ($10.99 at Lowe's) that turns the light on at 38 F.
Nick
This is Turtle.
Well first I see you don't work on hvac system and know what the run times are for a properly sized hvac system verses a cool down time for a indoor temp. of about 105ºf down to 70ºF to 75ºF . 8 hours you may save a little but at 4 to 6 hours of down time will cost you 4 to 6 hours of run time at 105ºF to get it back to the regular temp. inside. Also your going to waiting about 1 to 2 hour before you can stay in there when you come home.
Now if you have oversized hvac system like 5 tons on 1,500 sq. ft. house. Your answer would be ok, but a properly sized system would cost you big time on a 4 hour down time.
TURTLE
This is basic 300 year-old physics, Turtle. Turning an AC off for even 1 minute saves cooling energy :-)
But the AC setback still saves energy.
Nick
How would the house get from 70 F to 105 F in 8 hours on a 100 F day? Assuming it could (which would save lots of AC energy), and assuming it had resonable insulation, it would have very little thermal mass, so the AC could cool it back to 70 F very quickly.
The setback would still save energy, unless the AC becomes a lot less efficient (has a lower COP) with a higher indoor-outdoor temp diff.
A 1500 ft^2 house with 300 Btu/h-F of thermal conductance could warm from
70 F to 105 F in 8 hours on a 110 F day if RC = -8/(ln((105-110)/(70-105) = 4.1 hours, which makes C = 4.1x300 = 1200 Btu/F, not much. A 36K Btu/h AC might cool the house from 105 to 70 F in (105-70)1200/36K = 1.2 hours. Keeping the house 70 F for 8 hours would require 8(110-70)300/36K = 2.7 hours of AC operation... 1.2/2.7 is a 55% energy savings.Nick
Your technician was correct. He would determine if it was operating at
100% though use his gauge set for pressure measurements, and the temperatures measured on the evaporator and condensor coil surfaces to approximate this determination. If these are within the prescribed ranges, there likely is little need to top off the refrigerant charge in the system.So long as the freon in the system is at a sufficent level to continuously provide bubble free liquid in the high pressure line, it makes little difference in the operating characteristics of the air conditioning system.
In fact, larger industrial systems always include a view port in the liquid freon line to check for excess bubbles. Too many bubbles may also reflect a need for the addition of freon to the system or the installation of the system was faulty and contains trapped air.
A refrigeration gauge set is incapable of revealing this information, and indicates only that the pressures in the low and high pressure sides of the system are consistent with the particular variety of freon in use for the measured surface termperature on both the condensor and evaporator coils. It reveals very little helpful information about the adequacy of the freon charge in the system. Usually a pocket sized card for the freon in use (typically Freon-22 in small to medium size -- 3 to 30 tons -- central A/C systems).
On smaller home systems which lack a view port, most competent refrigeration techs will, after checking the operating pressures, charge the system up to the point where frost begins to appear on the evaporator low pressure tube fitting. This is the point of optimal cooling and presumably optimal system efficience.
I'm not a refrigeration engineer (although I am a physicist/engineer), but over the years (at least 30) I've maintained or installed some reasonable large refrigeration systems and air conditioners (some of which were two-stage special purpose systems capable of reaching test chamber temperature of below -80-degrees F), sever 30-60 ton air conditioning systems, and installed 3 central systems in homes that I've owned.
During these years, out of necessity I learned how to replace compressors, braze joints, pull a vacuum and "dry" the systes, employ leak detectors and repair leaks, all basic to the HVAC trade, consequently I'm pretty sure of the correctness of the info I post, and I would challenge any A/C or HVAC tech to specifically cite and correct any error. In fact, over 30 years I never had to employ an HVAC tech to correct any of my work. (In fact, it was the inadequance of the HVAC techs that I encountered that first cause me to get my hands dirty!)
Harry C.
p.s., Never SMOKE when you're working with freon. Any competent refrigeration engineer can explain to you why this precaution is needed, but your average HVAC tech is little more than a glorified plumber and likely hasn't a clue (unless of course his supervisor has informed him)!
Damn, you trade guys are good on arm waving pontification, but short on details.
Could it possibly be that all you know about the subject is what you were told in trade-schools, and not by a competetent, degreed engineer?
Why the reluctance to attempt and correct the specific errors you found? Lemme guess!
Harry C.
This is Turtle.
This all looks good on paper but in the real world with a over sized hvac system as you say a 3 ton on 1,200 sq. ft. house. A properly sized hvac system will have a 1.5 or maybe 2 ton at most on the 1,200 sq, ft. house. 3 ton 36K btu rating system when properly sized will never be on a 1,200 sq. ft. house.
Now you say the 3 ton 36K btu rating is used in your calculation here. All hvac system are rated at 95ºOutdoor temperature and when the ambiant goes above the
95ºF level your BTU rating falls a good bit to maybe 31K or 33K btu's at 105ºF outdoor temperature.Now with all your calculations that the hvac system is perfectly tuned and all coil are clean and serviced regularly. There was some research done in California on systems being properly charged with freon, Clean coils, and running at what they should be putting out. More than half was not operating at what they should have been and was not putting out the BTU rating stated by the manufactor. A lot of the system checked was running at about 70% of what they should be putting out.
Now to you have a big ass 3 ton hvac system on 1,200 sq. ft. house. I personally have a 2,250 sq. ft. home and cool it with a 3.5 ton 14 seer system. I have let my cooling system be off for being gone for about 8 to 10 hours and on a 105ºF day. My house inside went up to about 98ºf inside and when i turn on my perfectly tuned system on. It took 3.5 hours to pull the house back to 72 ºF. The first 2 hours you can not stay in there for it being too hot. Now if i would install a over sized hvac system and have a 5 ton or so. It would not be but a hour or so to get back down to 72ºF inside but I would have to deal with high humitity in the house and will have to run my system at lower temperature than
72ºF or maybe down to 65ºF to get the water vapor out of the house. With a 90%RH a house at 60ºF will feel very warm inside. With a 10%RH and 95ºF inside the house will feel very cold. If you don't properly size the system you will have a nitemare with %RH to deal with.Now here is one that will never fit with your calculation on the cooling of the house. All properly designed and sized hvac systems are designed and installed to have a 90% run time which are designed to be run all the time and not turn them off. On a properly sized / designed hvac system if you started at 100ºF inside temperature could easily have a 8 hour run time to get it cool enough to be called cool enough to live in it. So if it is designed correctly your theory is out the window. If you have a oversized system you could maybe somewhere near the recovery time needed to get the house back down in temperature, but with no humitity removial like it should be.
Now you had said a house inside with no air on will not go up to 100ºF+ with in
8 hours -- out in the direct sun light, 105ºF outdoors, Roof area temperatures running about 190ºF with the direct sun light on it, house with the average R-19 rating on it, and most all houses are not air tight. In 8 hour, I would be surprized to not see it 100ºF.Now one last point here. Your calculation will be for the air inside the house and not for the metal , cloth couches , Rugs / carpet, and furniture which will hold and release heat over the next 4 to 8 hours and you will have to remove this extra heat held by these items as the next 8 hours of operation time goes.
Nick i live in the real world and you must live in the Paper world.
TURTLE
Nick if you packed more sand in your ass you wouldn't fall over as much.
Just how often do you call criminals over so you get your reaming?
Dear Bill,
I am not indifferent to the depravity of your cravings.
May God have mercy on your soul.
Nick
There seems to have developed an ant-intellectual movement on the hvac newsgroups lately.
It's like the dummy's want revenge for someth>
Don, perhaps I could help you, boy. Maybe I could teach you something slightly technical, something that you could then make your own kind of original remarks on. Perhaps that'd make you feel a little better, being able to participate in these technical forums appropriately applying a little newly learned technical thought.
We should try, it might be quite therapeutic, you wouldn't feel so out of place here needing to side with idiots just because they have numbers and are so willing to accept you as one of their own.
It is to Nick, and a few others mind you, that I'm referring.
Nick calls us criminals in good humour. You only get offended because on top of being a complete technical loser yourself, you find it patronising that Nick expresses frustration that you duck right under that humour. Quite simply, you've lost it, you've taken yourself so seriously for so long that you've completely lost the plot.
I might be assuming here, but I would imagine that the only reason you attack Nick for the said patronising is because Paul leads you by example. I've known you on the net for a while, Don, you're not quite an individual, you're a follower, I just wish you'd have higher standards when it came to roll models.
lot of milligan followers here
and why follow the unemployed dude, who, like an ol woman, has a life revolving around cats
makes not a lot of sense
individual,
snip the razzamataz askew comment/s
...psychrometrics Harry, that, the Five Senses, plus a minimum 4 digit read current tester (tong meter) is all you need to check
99.9% of "my AC is hot" domestic claims. This thread was presented badly, answered worse, deteriorated to the troll posted here. I trust that is enough details for you Harry.You might want to enlighten me as to just *what I S* a
degreed engineer
as I have never heard of such an animal. Engineers (.au) have tertiary degrees issued after a University course in academic principles addressing Mechanical Services. Engineers write processes and 'cheat sheets'. We RefMechs (.au) OTOH have a degree of engineering **skill**, hence we are able to apply and interpolate psychrometrics in the field.
Most Engineers (.au) would have NFI as to the microcosms forming the substance of this thread,, though I do suspect their off-shore equivalents have attempted an answer here and there.
**That** is usually how things get FooBar'd..... out here in the booniesYou read as having a degree of certain eloquence Harry. Well it may be that you apply this degreed (sic) engineering to tasks at home buuuuuuuut please keep it in your own home and refrain from packaging the BS in ways that some poor sap may just , just believe your speak as Gospel.
cheers
BTZ
Don i am a citizen of both Canada and USA and have always had a job, and have never seen the likes of the whiners on alt.hvac in my travels
why do resi guys - which i could train a border collie to do- whine so much
maybe i would too, if was not smart enough to rise above resi havc
Er, I think there's some confusion here. Um, actually, the way it is, both Shaun and Paul have lives, okay. But it's not the same with jobs, you see, when it comes to employment, Shaun is employed, Paul is UNEMPLOYED. I just thought I should say so because it occurred to me that if your intentions were noble, that you wanted to help someone here, you might redirect the, perhaps disguised, benevolence in Paul's direction, to be specific I suggesting that perhaps you'd like to assist Paul in finding a job. You know, like finding someone that would employ him.
I hope this helps. Helps us all. Please god!
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