electric outlet for window AC question

| To each his own, but if you have the electrric power and the spare cash when | you buy a window unit, go for a larger size. "Efficiency" just ain't all | that important if all you are cooling is ONE room. >

However, given the constant problems I see with central air conditioning, I will be going with individual room air conditioning instead in my new house (designing now, build in a few years). There will be air ducts for air flow, but they won't be the distribution of cooling or heat, they will be for the distribution of fresh air and filtering. However, I will not be using window air conditioners. My grandfather added a room onto his house back in the 1960's and heated and cooled it with a vertical wall unit that was about 6 feet high. The exterior portion for expelling heat was right behind it (e.g. it probably had to be installed only on an exterior wall). Today's market has quite a number of "mini-split" units, which are basically a split A/C system of varying sizes down to small rooms. Many including heating as an option. And there are still many wall-sleave units on the market with heat.

| NEC - 20A receptacles are allowed on a 15 Amp circuits |> whether you like it or not., it is safe at the user or end level, Now |> Fuck Off ! |>

|> & The Hell with This Post it's way overdone....? | | Just use an extension cord | | Easy, Efficient and Affordable | | | By a cord rated at 20 amps, snip the plug end off, wire it direct into | a 20 amp breaker, plug the A/C in the other end and all done.

"Do not do this at home"

Absolutely do not do thus very unsafe and illegal thing at all, anywhere.

No, not really.

Yes, also in printing plants.

No, not at all.

No, as yo already pointed out, it is a fixed capacity, not variable. You are deluding yourself to thing you can change the capacity. Sort of like people that keep pushing up the thermostate to get the house heated faster when the heat is already running. The copressor is either on, or off. There is no varialble capacity.

I said properly sized. If it is too small, it is not properly sized is it? You will still get reduced humidity in any case.

You can certainly do that, but I am not sure it is wise. Normally what you suggest will cost more to install and operate (operation cost may be reduced if you carefully zone them). It also can be more noisy.

You may run into some issues with local zoning in some areas.

A well designed central system have few problems, likely fewer than a number of single room systems. If you read here, you will see the results of problem systems. We don't get questions about well designed and installed systems. We get very few question about the room units (as you are describing) but that is because they are not common.

There may well be some situations where the small units may be the best choice, but I would have to believe that would be a small percentage of locations.

|> You are being silly. If you have a fixed capacity window unit you can |> size |> it to be "too big" all the time (and play games with fan speed to adjust |> capacity) | | No, as yo already pointed out, it is a fixed capacity, not variable. You | are deluding yourself to thing you can change the capacity. Sort of like | people that keep pushing up the thermostate to get the house heated faster | when the heat is already running. The copressor is either on, or off. | There is no varialble capacity.

It is possible, though not always efficient, to vary the capacity of a heater. Two elements connected in parallel could be reconnected in series to have a lower temperature when the difference between desired and actual temperature of the air is small (1 degree).

Is there anything at all that can make the A/C coils be less cool than they would be at "full tilt"? One reason I want to know is that I see many cases of central A/C units freeze up; the coils are obviously very cold and apparently there is too much water and/or not enough air.

|> or get a unit that's too small some of the time and be downright |> miserable. I will gladly sacrifice a few "perfect" days to avoid a |> single |> "miserable" day | | I said properly sized. If it is too small, it is not properly sized is it? | You will still get reduced humidity in any case.

Having more capacity could, perhaps, reach desired temperature faster. But would an over capacity A/C tend to freeze up more?

In alt.engineering.electrical Joseph Meehan wrote: | snipped-for-privacy@ipal.net wrote: |> In alt.engineering.electrical John Gilmer |> wrote: |>

|>| To each his own, but if you have the electrric power and the spare |>| cash when you buy a window unit, go for a larger size. |>| "Efficiency" just ain't all that important if all you are cooling is |>| ONE room. >

|>

|> However, given the constant problems I see with central air |> conditioning, I will be going with individual room air conditioning |> instead in my new house (designing now, build in a few years). There |> will be air ducts for air flow, but they won't be the distribution of |> cooling or heat, they will be for the distribution of fresh air and |> filtering. However, I will not be using window air conditioners. My |> grandfather added a room onto his house back in the 1960's and heated |> and cooled it with a vertical wall unit that was about 6 feet high. |> The exterior portion for expelling heat was right behind it (e.g. it |> probably had to be installed only on an exterior wall). Today's |> market has quite a number of "mini-split" units, which are basically |> a split A/C system of varying sizes down to small rooms. Many |> including heating as an option. And there are still many wall-sleave |> units on the market with heat. | | You can certainly do that, but I am not sure it is wise. Normally what | you suggest will cost more to install and operate (operation cost may be | reduced if you carefully zone them). It also can be more noisy. | | You may run into some issues with local zoning in some areas.

What do you mean? Can you be more specific?

| A well designed central system have few problems, likely fewer than a | number of single room systems. If you read here, you will see the results | of problem systems. We don't get questions about well designed and | installed systems. We get very few question about the room units (as you | are describing) but that is because they are not common.

I would guess that the vast majority of installed central A/C are not properly designed and installed.

How would you design a central A/C/heat system to control each room to it's individual desired temp/RH? Consider each bedroom has individual control, and the kitchen is an excess heat source even if it has the same desired temperature setting as other rooms.

I suspect that zoning by means of controlled air flow (e.g. shut off the air to rooms that are already sufficiently cool) is a culprit in A/C coils freezing up because the zone system sometimes runs too little air past.

But I would never have a zoning system that is based on cutting air flow as the control means. So what else is there?

| There may well be some situations where the small units may be the best | choice, but I would have to believe that would be a small percentage of | locations.

I think my house will be a small enough percentage.

Defrost heaters.

One reason I want to know is that I see

The "usual suspect" is insufficient air flow to keep the coil temperature about freezing. When you can independently vary the speed of the "inside" and "outside" fans, then it's possible to control the humidity by running the fan at a lower speed until the humidity is reduce to a preset level. Any particular coil is limited in the amount of moisture it can remove (rather than the moisture condensing an then blowing back into the living space.)

Under certain circumstances, low refrigerant can cause the problem. When happens is that the pressure in the "low" side (the inside coil" get's so low that the little refrigerant that's left creates a small area in the coil that"s well below the freezing point of water. That part of the coil "freezes up" and insulates the coil there. The point where the refrigerant vaporizes in the coil continues along the junction between the ice and just liquid water. Usually, however, low refrigerant will cause "no cooling." This doens't happen often because the "cooling" capacity of a unit that's very low on refrigerant isn't much and ice does conduct a little heat.

Nope! It's thermostat will just shut off the compressor when the return air temperature falls below the set point. As others have notes, it will tend to short cycle.

>

Well, if I understand the limited amount of reading I have done on some of the newer split AC units (like the Mitsubishi "Mr. Slim"), they use a VFD to run the compressor. I *assume* that the coils would be less cool/more cool as the VFD varies. I hope someone who *knows* about these units will chime in with the facts.

Ed

I'm shocked to read that FireMan Tom would suggest that the NEC allows for a 15Amp device on a 20Amp protected circuit...It does Not Allow for that, & it is a violation albeit a mild one, but nevertheless improper & Not Recommended. All he's done is attack every reply i post here... and now he's just being ridiculous and harmful.He must think I'm some punk tech from his township., I've been doing Electrical Troubleshooting & Installations for over 30 years and seen plenty stupidity like that go unchecked because they believe in the " pros " that did it, and not in the letter of the codes and the wording of the specifications and experience.

After all: He is a Fireman, he lives for the Sinister Fire to take hold of your property so he can do his job., didn't know he'd stoop to that level though to insure future work. What happened to Better Safe than Sorry ?

Leave it alone; Get the proper sized Receptacle & Breaker for the new circuit you are running for your Air Conditioner. I'm through with this....... Roy

There are also solid-state proportional heater controls, that use phase-controlled thyristors to vary the heat output over a continuous range. Usually not cost effective for simple space heating, but often used where more precise temperature control is needed.

There is a lot I could go into in this area. The base temperature of the evaporator is determined by the saturation pressure of the refrigerant inside it. Advanced systems use a variety of suction pressure controls to maintain this saturation condition just above 32F. In a high-end system, suction throttle valves (a form of 'back-pressure' regulator) will maintain the saturation temperature in the evaporator at between 35 and 45 F. This is cold enough to condense a lot of the water vapor, but will still leave some in the air. When air is at 100% RH at 40F, and then warmed back to 70 F, it will be about 50% RH.

Another pressure control method is various forms of 'staging' in the compressor, or the use of variable speed compressors. By controlling the amount of pumping the compressor does, the evaporator pressure is kept above freezing. Interestingly, in modern auto A/C, there is a suction pressure switch that cycles the compressor on/off by engaging/disengaging the clutch used to drive it. Of course, cycling a motor driven compressor on/off is not viable as it would have to do this several times a minute, and the repeated high starting currents will burn out the motor.

Contrary to urban myth, the TXV (ThermoeXpansion Valve) is *NOT* used to prevent freezeups. It works by sensing both the pressure and temperature at the evaporator outlet, and is used to control the amount of superheat in the refrigerent as it leaves the coil. A small amount of superheat is desired to prevent the compressor from ingesting liquid (that would damage the compressor). But amateurs will often 'fiddle' with the TXV when either the unit freezes up or doesn't cool properly.

One cause of freeze-ups is too little charge in simple capillary units (no TXV). The lower pressure in the system causes the evaporator to run at lower temperatures.

And finally, despite what I wrote above, there *are* some cheap units that are designed to have the evaporator running below 32F. These cheap units rely on a high air flow to keep the evaporator warm enough to avoid a build up of frost. They don't work well in humid climates. The best you can do with these is to make sure the air flow is unobstruted by dirty filters.

daestrom

How do you explain the common, and 'allowed' practice of using several 15A receptacles on a branch circuit with 12AWG wire and a 20A circuit breaker??

Mind you, that is *not* for the dedicated circuit we're talking about here. A dedicated, single outlet circuit should have a 20A receptacle for a 20A circuit.

daestrom

We might be talking two different zones here. I am talking about local governmental regulations. In some areas they regulate window/thrugh the wall A/C units. Sometimes they only allow them on certain sides of the home or they require certain distance to a property line etc.

Sad to say I agree.

A proper design and if needed zoning can do it. Each situation is different and calls for different solutions. I am only suggesting that anyone would be wise to consult a qualified professional to offer their opinion on the best solution for any given case. Restricting their solutions is counter productive for the home owner. On the other hand if you approach it by asking them to consider independent room equipment I believe that may open up a solution that they might not have considered as I doubt if most people would want it.

In a poorly designed system, yes. In a properly designed system no.

So even if it were properly designed you would reject it?

Roy Your assertion that the US NEC forbids the installation of fifteen ampere devices on twenty ampere circuits is simply not supported by the codes language. If you believe it is you could at least quote chapter and verse when trying to convince the rest of us. Perhaps you are trying to make a distinction between listed devices that have been tested to carry fifteen amperes and fifteen ampere patterned devices. All fifteen ampere patterned duplex receptacles that are listed by recognized testing laboratories in the US are tested to carry twenty amperes between their screw terminals. If the code did in fact forbid the installation of devices with a rated ampacity less than the circuits ampacity then every home in the country is in violation. If you look at the marked ampacity of light switches you will see that most are tested to carry less than the circuits of which they are installed. The code only requires that switches be rated for the load that they are installed to control.

That the US NEC allows multiple fifteen ampere patterned receptacle devices on a twenty ampere circuit was never in question. The question was did the code permit a single twenty ampere patterned receptacle on a fifteen ampere circuit. The actual language of the US NEC on that issue is;

210.21 Outlet Devices. Outlet devices shall have an ampere rating that is not less than the load to be served and shall comply with 210.21(A) and (B). (B) Receptacles. (1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

So working from the actual language of the code I concluded that the code does not in fact prohibit the installation of a twenty ampere patterned receptacle on a fifteen ampere branch circuit as the only receptacle on that circuit. Your assertion that I recommended this practice is drawn from thin air as I never said that in this or any other forum.

In alt.engineering.electrical John Gilmer wrote: | |> Is there anything at all that can make the A/C coils be less cool than |> they would be at "full tilt"? One reason I want to know is that I see |> many cases of central A/C units freeze up; the coils are obviously very |> cold and apparently there is too much water and/or not enough air. | | The "usual suspect" is insufficient air flow to keep the coil temperature | about freezing. When you can independently vary the speed of the "inside" | and "outside" fans, then it's possible to control the humidity by running | the fan at a lower speed until the humidity is reduce to a preset level. | Any particular coil is limited in the amount of moisture it can remove | (rather than the moisture condensing an then blowing back into the living | space.)

If you have a zone control system that shuts off selected air ducts, then you can easily end up with insufficient air flow.

| Under certain circumstances, low refrigerant can cause the problem. When | happens is that the pressure in the "low" side (the inside coil" get's so | low that the little refrigerant that's left creates a small area in the coil | that"s well below the freezing point of water. That part of the coil | "freezes up" and insulates the coil there. The point where the refrigerant | vaporizes in the coil continues along the junction between the ice and just | liquid water. Usually, however, low refrigerant will cause "no cooling." | This doens't happen often because the "cooling" capacity of a unit that's | very low on refrigerant isn't much and ice does conduct a little heat.

I've seen this happen before, too.

| I'm shocked to read that FireMan Tom would suggest that the NEC allows | for a 15Amp device on a 20Amp protected circuit...It does Not Allow for | that, & it is a violation albeit a mild one, but nevertheless improper & | Not Recommended. All he's done is attack every reply i post here... and | now he's just being ridiculous and harmful.He must think I'm some punk | tech from his township., I've been doing Electrical Troubleshooting & | Installations for over 30 years and seen plenty stupidity like that go | unchecked because they believe in the " pros " that did it, and not in | the letter of the codes and the wording of the specifications and | experience.

Receptacle devices conforming to NEMA 5-15R and 6-15R configurations really _are_ "rated" at 20 amps, even though they will refuse to accept plugs for appliances with NEMA 5-20P and 6-20P configurations.

They really are 20 amp devices if they have a legitimate UL listing. In reality, they (at least the good ones) will survive a sustained 30 amp load (maybe even more), as long as there are no hot spot or arcing contact problems in the connected wiring.

| Leave it alone; Get the proper sized Receptacle & Breaker for the new | circuit you are running for your Air Conditioner. | I'm through with this.......

Now you have time to get your meds refilled.

"Easily?" Nah!

It can happen but simple stuff like a thermostat in the main distribution duct (before the dampners) that would either shut off the compressor or over ride a "decision" to close a dampner can "solve" that problem.

If ALL zones are satisfied, the compressor should shut down in any case.

>

In alt.engineering.electrical Joseph Meehan wrote: | snipped-for-privacy@ipal.net wrote: |> In alt.engineering.electrical Joseph Meehan |> wrote: |>| You may run into some issues with local zoning in some areas. |>

|> What do you mean? Can you be more specific? | | We might be talking two different zones here. I am talking about local | governmental regulations. In some areas they regulate window/thrugh the | wall A/C units. Sometimes they only allow them on certain sides of the home | or they require certain distance to a property line etc.

I'm sure there will be, in some areas, sound abatement rules would apply to any external device, including the unit for a central A/C, or a home generator.

Getting them on the side of the house facing away from the sun as much as possible would be a good idea, but I don't see a particular need for it to be a regulatory issue, other than in California where there is a severe shortage of power generation capacity due to improper planning at the state government level.

|>| A well designed central system have few problems, likely fewer |>| than a number of single room systems. If you read here, you will |>| see the results of problem systems. We don't get questions about |>| well designed and installed systems. We get very few question about |>| the room units (as you are describing) but that is because they are |>| not common. |>

|> I would guess that the vast majority of installed central A/C are not |> properly designed and installed. | | Sad to say I agree.

And how much would it cost to get one to be well designed for 12 zones? This would have to be a design that sustains air flow in all zones.

|> I suspect that zoning by means of controlled air flow (e.g. shut off |> the air to rooms that are already sufficiently cool) is a culprit in |> A/C coils freezing up because the zone system sometimes runs too |> little |> air past. | | In a poorly designed system, yes. In a properly designed system no.

The only zoning systems I have seen do it by shutting off air flow to the zones not to be cooled. And given that I will need at least 8 zones, possibly as many as 12, I suspect this will be a problem.

OTOH, zoning by means of several smaller "central" style A/C systems might still be feasible.

But one issue is that I need to have the air flow in each room whether or not that room needs a temperature change. If I use mini-splits in all the rooms, I'd still have the central air flow ducting in place with a passive blower. But I'd prefer connecting them together somehow if I can find a way, where the room unit has air fed from that central air flow system.

|> But I would never have a zoning system that is based on cutting air |> flow |> as the control means. So what else is there? | | So even if it were properly designed you would reject it?

Not necessarily. I'm just very skeptical that it can really happen. I'm not planning my house design around the prospect of a proper design being feasible.

|> If you have a zone control system that shuts off selected air ducts, then |> you can easily end up with insufficient air flow. | | "Easily?" Nah! | | It can happen but simple stuff like a thermostat in the main distribution | duct (before the dampners) that would either shut off the compressor or over | ride a "decision" to close a dampner can "solve" that problem. | | If ALL zones are satisfied, the compressor should shut down in any case.

But what if one zone needs cooling?