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Old 04-26-13, 02:42 PM   #31
AC_Hacker
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...as time and money allow I will certainly be working on projects.
Those all sound like really great efforts.

You should put some photos up for others to see.

Best,

-AC

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Old 04-27-13, 12:52 AM   #32
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"Another question, would running the A/C in the cooler temps of the night be more efficient for it? Last question, would running the A/C once for an hour be more efficient than running it for 3 20 minute periods over 2 hours. Basically is start up power enough that running the A/C fewer cycles but longer periods would amount to anything?"

Yes.

My air conditioner is a cheap not too efficienct unit from 1986. Here is the power input to my 22,000BTU/hr air conditioner for different outdoor temperature ranges when the sun isn't pointing at the unit. This includes the furnace blower as well as the compressor so you are seeing the whole system.
77-81+? 2400 watts
68-76 2300 watts
60-68 2200 watts
<60 2100 watts

Not only does the lower outdoor temperatures cause less power to be used by my unit, if I operate the air conditioner at colder than 60 degrees outside and the supply temperature isn't warmer than 80 degrees, the coil will freeze. I've frozen the lines going all the way back to the condenser twice from evaporator icing. If you aren't familiar with your system, try to keep it from running when it is cooler than 65 degrees outside. In my case I should install a freeze thermostat to the evaporator coil but I'm really not interested in throwing money away at trying to save an old inefficient unit that took the abuse twice already so I'm just more careful.

Basically what I'm saying is that the evaporator temperature is also lower along with lower power consumption which allows for better humidity removal. My supply registers have a measurably colder difference between indoor ambient to supply temperature. What this means is better efficiency.

Runtime, last summer I made sure to run my air conditioner 2 hours at the coldest point of the night as long as the temperature didn't have a threat of getting below 60 degrees outside. Dew points were extremely high last summer so opening the windows would actually increase the energy bill in the end and cause basement mold where I live. 20-30 minutes is just about the time that your evaporator is covered in water and is starting to drain off to remove the humidity from your house. In my case it is 30 minutes and I run the unit for 2 hours to try to remove as much moisture from the house as possible overnight so that the output of the unit when it is using more power is going to the sensible load(temperature) rather than the latent load(moisture removal).

266kwh $40.33 was my highest electric bill last year. Temperatures weren't where most people would like it but I was comfortable because I was able to sap the moisture from the air effectively and use a fan appropriately. This year the bills will be significantly higher because I'm not sharing the house with a picky female and I don't know if I can allow the evening temperature to rise enough to run a nightly 2 hour run without dropping the temperature below where I really want it. Her picky nature with the heat has this extreme conservationist a bit on edge over what will happen in the summer, hoping she's just a coldbaby.
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Old 04-27-13, 08:23 AM   #33
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Wow thanks for that info! Just another reason to figure out how to shift my peak load into the night hours.
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Old 04-27-13, 02:55 PM   #34
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Default Throwing money away?

Quote:
Originally Posted by MN Renovator View Post
"Another question, would running the A/C in the cooler temps of the night be more efficient for it?"...

Yes.

My air conditioner is a cheap not too efficienct unit from 1986. Here is the power input to my 22,000BTU/hr air conditioner for different outdoor temperature ranges when the sun isn't pointing at the unit. This includes the furnace blower as well as the compressor so you are seeing the whole system.
77-81+? 2400 watts
68-76 2300 watts
60-68 2200 watts
<60 2100 watts

Not only does the lower outdoor temperatures cause less power to be used by my unit, if I operate the air conditioner at colder than 60 degrees outside and the supply temperature isn't warmer than 80 degrees, the coil will freeze. I've frozen the lines going all the way back to the condenser twice from evaporator icing. If you aren't familiar with your system, try to keep it from running when it is cooler than 65 degrees outside. In my case I should install a freeze thermostat to the evaporator coil but I'm really not interested in throwing money away at trying to save an old inefficient unit that took the abuse twice already so I'm just more careful...

What this means is better efficiency.

Runtime, last summer I made sure to run my air conditioner 2 hours at the coldest point of the night as long as the temperature didn't have a threat of getting below 60 degrees outside... This year the bills will be significantly higher... I don't know if I can allow the evening temperature to rise enough to run a nightly 2 hour run without dropping the temperature below where I really want it... the heat has this extreme conservationist a bit on edge over what will happen in the summer.
This sounds like a clear case for improvement over the status quo. If you are not getting enough dehumidification with what you have now, swap out that cap tube for a TXV. At low outdoor temps, the unit will move much more latent heat outdoors and not freeze your evaporator. Your power consumption will rise slightly in proportion while the unit is running, but overall your run time will drop. At daytime temps, this option will pay for itself quickly by matching your indoor coil load with all that the condensor can supply, again reducing run time.

If you don't want to mess with the refrigerant circuit, increase the airflow at night. Just find a higher rated blower for your air handler and wire the speed taps to a 3-way light switch. The evap will not freeze up at night while the unit is running at max airflow. Depending on... blah blah detail detail ... the system will still pull just as much water out of the air at night while cooling the air like it is supposed to. This option will not save you as much money, but is easier to accomplish with less work involved. But you'll have to flip the switch for night speed.

Or you can always just go and buy a 20 seer ac unit and have someone else put it in. This may or may not be considered throwing away money since the unit would eventually pay for itself in energy savings. Especially if you went and bought a heat pump.

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Old 04-27-13, 04:39 PM   #35
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Scottorious,

You mentioned earlier that you have gray-water cistern on your property. I can't help but think that this would be a huge source of thermal mass for your idea. You may not need to load up your living space with tons of water to acheive your cooling needs during the day. Could you humor me and elaborate on the cistern?
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Old 04-27-13, 06:27 PM   #36
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Default Evaporative roof cooling...

Try putting a soaker hose along the ridge of your roof, and controlling the hose with a garden hose timer.

The idea is to let the evaporation do the cooling.

-AC
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Old 04-27-13, 10:38 PM   #37
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Ive considered the roof cooling.

The cistern is about 4 feed wide with the surface of the water at about 18 feet. I don't really know how deep it goes. Just an old brick cistern. Access at the top is only about 5 inches wide though. My house is on city water now but used to be on a well. I just got the well running again to use it to water my garden plus it looks really cool when its running. I don't know how anti-green this is but I had thought about using the pre-existing pump I have on the well to draw water out and use it for some type of cooling and discharge it into the cistern.
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Old 04-28-13, 05:50 AM   #38
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Now that sounds awesome! Use the cool well water as your source, pump it to your choice of air cooler in the basement, then run the somewhat warmed water upstairs to another air cooler. Discharge the warmed water to wherever it would be most useful. Set up the water pump to run off of your picaxe using temp differential control above an indoor temp setpoint.
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Old 04-28-13, 08:46 AM   #39
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just some sort of heat exchanger? radiator?
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Old 04-28-13, 09:08 AM   #40
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Quote:
Originally Posted by jeff5may View Post
Now that sounds awesome! Use the cool well water as your source, pump it to your choice of air cooler in the basement, then run the somewhat warmed water upstairs to another air cooler. Discharge the warmed water to wherever it would be most useful. Set up the water pump to run off of your picaxe using temp differential control above an indoor temp setpoint.
Yeah, that's a great way to look at it, kind of through an 'exergy' lens... using the appropriate heat energy (or in this case 'cool energy') at different steps as the energy cascades it's way down to an unusable entropy level.

That's a very sophisticated approach. There is even a book that is no longer easy to get called, "Low Temperature Heating and High Temperature Cooling REHVA Guidebook". You might be able to find it in libraries somewhere (inter-library loan). There was considerable work done on this front in Europe. A consortium called LowEx was formed and there was a broad effort to get other countries involved, including the US, who declined to get involved (you can lead a horse to water, but it's still a horse).

As far as I can see, the Europeans have internalized the lessons learned and are applying them to their approaches to heating & cooling.

I started a thread on EcoRenovator as a repository for information and discussion on this topic. The entry that has the most useful links to information is HERE.

I have searched for and found papers that detail 'Exergy Analysis' of heating and cooling projects. Most of the papers I have found at the time of my searches seem to come from Germany, Denmark, India and China.

Best,

-AC

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