Alternative Air Conditioner -- Your Ingenuity Required

stoneunhenged

I have a fairly unique set-up with some specific demands for cooling. Your expertise is welcome and needed. Here's the deal:

I live on a farm. I'm building a stand alone office for the farm operation. For five months of the year the average monthly high ranges from 88° to 92°. Humidity is high.

The office is in a 20' shipping container. The dimensions are 8'x8'x'20'. Interior volume is 1280ft³. The container is hyper-insulated with 2x4 stud framing on walls and 2x6 stud framing on ceiling, sheathed in drywall, with closed foam insulation sprayed to fill voids. PV panels will cover and shade the entire roof of the container. One long wall of the container is oriented south and exposed to the sun.

The container must be cooled to be habitable from May through September. I've looked at several design concepts for a PV-based system to power an ultra-efficient split air conditioning unit, and if I have to go in that direction I'm willing to spend the money to do it. (Yes, it's a lot of money.) But, it strikes me that there may be a better, less conventional way to go on this that is far less expensive and has much lower energy demands.

The container is located just 50' from a water well. The well has a static head of about 100'. It is currently pumped using a set-up designed and purchased from our friends at NAWS. Essentially, the volume of water is unlimited, and the temperature of the water from this depth is a constant 68° year round. I also have an unlimited ability to dispose of water pumped from the well. It can be directed to specific agricultural uses (livestock watering and irrigation) and ultimately percolates into the ground and back into the aquifer.

Here's my question: Why can't I pump the cool groundwater through a radiator located inside the container --a radiator through which air is blown by a fan-- and cool down the container? The outflowing water from the radiator would be piped outdoors and simply discharged on pasture, in gardens, or used for livestock watering.

Would this work? The temperature differential between the groundwater and the ambient temperature on the hottest days would be more than 32°. I assume I would need some form of condensation collector beneath the radiator to collect water produced when the warm humid air hits the cooler radiator fins.

A few questions:

How to size the radiator and rate of water flow?

How about the rate of air flow?

Any guess as to the energy efficiency of this system as compared to a split air conditioning unit?

Is there a way to convert this discussion to Btus, as in, Btus needed to cool this space and Btus produced by the cooling system described here?

What is the most energy efficient pump set-up for this scenario?

Sorry about the lengthy explanation, but I figured many of these details are relevant.

Thanks, dudes. I await your insight.

solar_dave

Re: Alternative Air Conditioner -- Your Ingenuity Required

Wouldn't the cost to pump the water be higher than operating the mini split? I suppose if you have a demand for the water anyway it might be a great add to minimize the load on the mini split. The only question is can you align the demand for the water to the demand for cooling in your office?

icarus

Re: Alternative Air Conditioner -- Your Ingenuity Required

Have you actually done a cooling load calc? Perhaps a small window unit might be small enough to effectively cool the unit? I have a cheap 500 watt unit that I run very occasionally off my Honda eu 1000, which could run on a smallish PV system. The money saved on the AC unit might pay for the PV system to run it.

Tony

Vic

Re: Alternative Air Conditioner -- Your Ingenuity Required

stone,

Am NOT an expert on these things, and recall the previous discussion o n the container ...

Think that you do not have enough temp differential to dehumidify, or cool efficently. Your radiator would probably need to be huge to be able to extract much cool from the water, and, therefore there would not be much dehumidification.

As "superinsulated" as 2X4 framing can be, is still not very well insulated. If you could berm a structure (or container), this would help keep some heat away from the structure. There can be a surprisingly large amount of heat radiated from the ground surrounding a building, that needs to be dealt with, in addition to the ambient temps. Whatta I know ? Good Luck, Vic

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

At 68 deg water Temperature it would be a good candidate to have someone build you a condensing coil and use water as the medium of heat transfer instead of Air and fan. You can build a tube inside tube of coiled copper. Say a 9,000 btu would only take about 6 foot or so with a 500 GPH water flow. The Refrigerant tube would be say 3/8 in. and the outside water tube could be 3/4 in. Another way is to put the coil in a container tray and pump the water in and let it over flow out a drain.

The question is the pumping cost. Say on a Boat Marine heat pumps work this way, but the pumps are only 1/20 hp and 1 Amp because the have no head to lift against, this way it's a no brainier to use the water.

Generally once the water temps are below 50 and above 75 the efficiency begins to go away.

stoneunhenged

Re: Alternative Air Conditioner -- Your Ingenuity Required

Thanks for the input. I'd be interested in more details about how the condenser coil might work.

Here are my calculations on the total space cooling load using a methodology I found on the web. Feel free to pick apart.

I'm using a 2.5 heat load multiplier for this exercise. You would use a 1.0 for a residential application, 1.2 for an office, 1.5 for a classroom, 2.5 for factory assembly work, etc. The container will be used as an office but I'm going to assume that it will have an unusually large thermal load because it is a steel box.

Anyway, given the dimensions and use and the differential in temperature between the groundwater (68°) and the desired interior temperature (74°), I would need to generate 2,592 Btus per hour in heat absorption. Since one Btu equals heating one pound of water one degree F, then if the system were perfectly efficient I would need to run 52 gallons of water per hour through a heat exchanger to achieve the desired cooling effect. (One gallon of water is 8.33 lb., and each pound of water in the system is 6° cooler than the desired temperature.) I'm going to assume about a 50% efficiency ratio, so let's say I'd need to pump 100 gallons per hour through a large heat exchanger. Bear in mind that this estimate assigns a very large thermal load to the structure and a modest efficiency ratio for the heat exchanger.

If I use an efficient Grundfos solar pump, it would take an average of about 5-10 minutes of pumping per hour to provide the needed 100 gallons of water. The water could be stored in a pressurized tank and be discharged in a steady metered flow to the heat exchanger. A pusher or puller fan could force air flow through the heat exchanger with a fairly small commitment of electricity. This set-up --a water pump running a fraction of each hour and an efficient fan-- strikes me as requiring far less electricity than even an efficient split air conditioning unit. And, the groundwater system is very adaptable (just pump more water if more cooling is needed) and can be used as a heat source in the winter.

Thoughts?

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

Here is a Link to a .pdf that will give you some information. I like the tube in tube because there is no dissimilar metal involved and galvanic corrosion it not a problem. I have made a couple out of 5000 btu window AC units, they work great. Doing a heat pump is no different., just reversing the load on the coil. In the summer you are cooling the refrigerant and in the winter you are warming it. The amount of tube ( length ) is going to depend on the total BTU capability of the condensing unit. The one I made was for a 6,500 but unit and it's 14 " in diameter. I slipped the 3/8 copper inside the 3/4 and wound it on a 5 gallon bucket. I slipped a tee on ends of the 3/4 and drilled a cap for the 3/8 and slipped it over slid it down and silver soldered it in place. I reduced the 3/4 tee down to 1/2 and connected the water in and out lines. The 3/8 lines are connected to the condensing unit. You have to solder them in place, pull a vacuum on the unit and re-fill with refrigerant. You can remove the fan and install something to control the water flow. With a small pump you can wire it in place of the fan, large pump you need a solenoid valve of some kind.

http://www.mcquay.com/mcquaybiz/literature/lit_systems/engnews/1002.pdf

stoneunhenged

Re: Alternative Air Conditioner -- Your Ingenuity Required

Could not get the mcquay link to work.

BB.

Re: Alternative Air Conditioner -- Your Ingenuity Required

Try BlackCherry's link again... I have fixed it (I think this is the one he was pointing to):

http://www.mcquay.com/mcquaybiz/literature/lit_systems/engnews/1002.pdf

-Bill

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

Thank You Bill !! Those split units seen to be pretty efficient as they are. The fans are variable and they have a better sensor system then most units have. One thing you can eliminate is a defrost cycle and you eliminate the exstream's . Once a air /air heat pump gets in the low 20's you don't get that much in heat. If I was using axillary heat coils, I'd consider it, otherwise it might not be worth the trouble.

techntrek

Re: Alternative Air Conditioner -- Your Ingenuity Required

Blackcherry04 wrote: »

Once a air /air heat pump gets in the low 20's you don't get that much in heat.

Not true for the mini-splits, especially the Mitsubishis which can extract useful heat down to -18 F if I remember right.

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

techntrek wrote: »

Not true for the mini-splits, especially the Mitsubishis which can extract useful heat down to -18 F if I remember right.

I am not touching that statement, I'll let someone that has one that operates in lower temperatures tell what they get out of one. While they are much better than a conventional Heat Pump there comes a point that it's not possible to create enough heat to be comfortable. I mean if you have the thermostat set to 70 deg and the air coming out is 71 deg it's producing heat, but you wouldn't be very comfortable. The big news with Sanyo is they added a Heat Strip inside, that tells me something.

techntrek

Re: Alternative Air Conditioner -- Your Ingenuity Required

Obviously you haven't read the multi-mega-page thread floating around here about mini-splits. Most recent posts from the last week touch on this very subject. I'll leave it to you to find it and read. Hint, two people "that has one that operates in lower temperatures tell what they get out of one".

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

techntrek wrote: »

Obviously you haven't read the multi-mega-page thread floating around here about mini-splits. Most recent posts from the last week touch on this very subject. I'll leave it to you to find it and read. Hint, two people "that has one that operates in lower temperatures tell what they get out of one".

Hint, I don't care, as I said. please feel free to post anything you'd like about them. Hint, If you choose to Google them you can find lots from users. It's not a contest I care to get into.

rplarry

Re: Alternative Air Conditioner -- Your Ingenuity Required

If it was me, I would just try using an automotive type radiator and a 12v fan, they make them specifically for radiators. Cool water in at the top and waste water out the bottom. If one is not enough then add another. If this is for an office where customers will be coming in then it might not be aesthetically pleasing. If just for you, then maybe you can live with it.
Larry

bmet

Re: Alternative Air Conditioner -- Your Ingenuity Required

I have asked about automotive radiator fans before, and the response was that they are power hogs. They come on instantly, with enough torque to blow gravel in your face. The Current required could be huge.

rplarry wrote: »

If it was me, I would just try using an automotive type radiator and a 12v fan, they make them specifically for radiators. Cool water in at the top and waste water out the bottom. If one is not enough then add another. If this is for an office where customers will be coming in then it might not be aesthetically pleasing. If just for you, then maybe you can live with it.
Larry

techntrek

Re: Alternative Air Conditioner -- Your Ingenuity Required

Blackcherry04 wrote: »

Hint, I don't care, as I said. please feel free to post anything you'd like about them. Hint, If you choose to Google them you can find lots from users. It's not a contest I care to get into.

LOL, you are funny.

The posts in the other thread prove you wrong - two Mitsubishi owners just posted about their very comfortable 9 F and 11 F (outside temps) experiences. Quite a bit colder than the "low 20's". The Sanyos aren't comparable, their ratings only go down to 5 F max, the Mitsubishis are a different animal.

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

Is this Thread about Alternative Air Conditioning and 68 deg water ?? or did I mis-read the title and it was about Mini-Split Heat Pumps ?? Thats what I thought, I was correct. There appears to be some thread drift from someone that is here to hassle other posters and disrupt the thread. It seems like there are other Threads that have ongoing discussion about them for someone that is interested in them. Hint, Hint

techntrek

Re: Alternative Air Conditioner -- Your Ingenuity Required

Let's see, there were four posts that mentioned mini-splits, including two from the original poster (including the first post of this thread) and yourself, before I jumped in.

XRinger

Re: Alternative Air Conditioner -- Your Ingenuity Required

Blackcherry04 wrote: »

Thank You Bill !! Those split units seen to be pretty efficient as they are. The fans are variable and they have a better sensor system then most units have. One thing you can eliminate is a defrost cycle and you eliminate the exstream's . Once a air /air heat pump gets in the low 20's you don't get that much in heat. If I was using axillary heat coils, I'd consider it, otherwise it might not be worth the trouble.

The old 24k BTUh 24KHS72 Sanyo (ASHP)Mini-splits work pretty well. I think both of mine do better than the spec..
Attachment not found.
It got pretty chilly here back on Dec 18-19 and we were warm as toast..( If the toast was 20C).





We just started using two units this winter. It's going to be interesting to see
if we are going to need back-up heating when it gets down to -15C..
I guess it's going to depend on the amount of heat loss in the house.

This year, when it gets really cold at night, I'm also going to try lowering the temperature setting down to 17 or 18 C.
Which will still be good for sleeping.. We'll just sleep-in until the sun comes up, and we start getting some solar gain.
Hope it's not real over-cast!

Cheers,
Rich

stoneunhenged

Re: Alternative Air Conditioner -- Your Ingenuity Required

rplarry wrote: »

If it was me, I would just try using an automotive type radiator and a 12v fan, they make them specifically for radiators. Cool water in at the top and waste water out the bottom. If one is not enough then add another. If this is for an office where customers will be coming in then it might not be aesthetically pleasing. If just for you, then maybe you can live with it.
Larry

Actually, I think I'm going to try a version of this idea using a 24"x24" heat exchanger and a quiet, efficient DC fan (not one designed for a car radiator). I'll put an inline flow meter and play with the flow rate to optimize cooling.

LucMan

Re: Alternative Air Conditioner -- Your Ingenuity Required

stoneunhenged wrote: »

I have a fairly unique set-up with some specific demands for cooling. Your expertise is welcome and needed. Here's the deal:

I live on a farm. I'm building a stand alone office for the farm operation. For five months of the year the average monthly high ranges from 88° to 92°. Humidity is high.

The office is in a 20' shipping container. The dimensions are 8'x8'x'20'. Interior volume is 1280ft³. The container is hyper-insulated with 2x4 stud framing on walls and 2x6 stud framing on ceiling, sheathed in drywall, with closed foam insulation sprayed to fill voids. PV panels will cover and shade the entire roof of the container. One long wall of the container is oriented south and exposed to the sun.

The container must be cooled to be habitable from May through September. I've looked at several design concepts for a PV-based system to power an ultra-efficient split air conditioning unit, and if I have to go in that direction I'm willing to spend the money to do it. (Yes, it's a lot of money.) But, it strikes me that there may be a better, less conventional way to go on this that is far less expensive and has much lower energy demands.

The container is located just 50' from a water well. The well has a static head of about 100'. It is currently pumped using a set-up designed and purchased from our friends at NAWS. Essentially, the volume of water is unlimited, and the temperature of the water from this depth is a constant 68° year round. I also have an unlimited ability to dispose of water pumped from the well. It can be directed to specific agricultural uses (livestock watering and irrigation) and ultimately percolates into the ground and back into the aquifer.

Here's my question: Why can't I pump the cool groundwater through a radiator located inside the container --a radiator through which air is blown by a fan-- and cool down the container? The outflowing water from the radiator would be piped outdoors and simply discharged on pasture, in gardens, or used for livestock watering.

Would this work? The temperature differential between the groundwater and the ambient temperature on the hottest days would be more than 32°. I assume I would need some form of condensation collector beneath the radiator to collect water produced when the warm humid air hits the cooler radiator fins.

A few questions:

How to size the radiator and rate of water flow?

How about the rate of air flow?

Any guess as to the energy efficiency of this system as compared to a split air conditioning unit?

Is there a way to convert this discussion to Btus, as in, Btus needed to cool this space and Btus produced by the cooling system described here?

What is the most energy efficient pump set-up for this scenario?

Sorry about the lengthy explanation, but I figured many of these details are relevant.

Thanks, dudes. I await your insight.

I don't want to get into a long drawn out discussion on cooling and thermodynamics so i'll get to the point.
68 degree water is not going to do it for you no matter how many GPM you put through a heat exchanger. You need 42-45 degree water for cooling and dehumidification. That's the water temp commercial chillers run. The lowest temperature that you might achieve with 68 degree water is 83 degrees.
There will be little or no dehumidification at that temp. Do a search on dew point.
An 18-24K BTU A/C unit of your choice will do the trick.
If you can swing it, go with a minisplit inverter unit, if not go with a window or through the wall a/c. Just stay away from the Amana units. Panasonic makes a nice 18k window unit.

Shadowcatcher

Re: Alternative Air Conditioner -- Your Ingenuity Required

Geothermal heat pumps work quite well and are more efficient than an air to air even when ground water temp is not low enough to just run through a cooling coil. The question is what is the ground water temperature one source http://www.enoscientific.com/groundwater-temp-map.htm

SteveK

Re: Alternative Air Conditioner -- Your Ingenuity Required

LucMan said it....

Folks, there is no problem with a mini-split for heating in down low outdoor temps. The Mitsubishi H2i units provide full capacity at 5F...without any resistive heating elements. They will cool your shipping container nicely. They also have a dehumidifier mode which does not cool down the room much at all if selected.

When investigating geothermal we were told that reliability and maintainence were real concerns especially if it were truly a well fed system.

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

techntrek wrote: »

Not true for the mini-splits, especially the Mitsubishis which can extract useful heat down to -18 F if I remember right.

techntrek wrote: »

LOL, you are funny.

The posts in the other thread prove you wrong - two Mitsubishi owners just posted about their very comfortable 9 F and 11 F (outside temps) experiences. Quite a bit colder than the "low 20's". The Sanyos aren't comparable, their ratings only go down to 5 F max, the Mitsubishis are a different animal.

I am still waiting on the one that works at -18 degrees Fahrenheit. That is the one that will change the world . Going from -18 F to + 5 deg's or +9 degrees is a long way from the -18 F .

XRinger

Re: Alternative Air Conditioner -- Your Ingenuity Required

Shadowcatcher wrote: »

Geothermal heat pumps work quite well and are more efficient than an air to air even when ground water temp is not low enough to just run through a cooling coil. The question is what is the ground water temperature one source http://www.enoscientific.com/groundwater-temp-map.htm

Yeah, GSHPs are more efficient.And they are super effective during sub-zero weather.
But are they price efficient? When you factor in the cost of installing a giant ground loop in the backyard,

Depending on where you live, you just might find it's going to take more than a few years to recover the difference. Diff = $GSHP - $ASHP installed.
Since the yearly operating cost of the ASHP (mini-split) is So close to the cost of running the GSHP..

We are lucky here in the Boston area, the average temperatures of the coldest months of the year is about 25 F. (Inside my Sanyo's zone).
Attachment not found.
From "City Data" website.

stoneunhenged

Re: Alternative Air Conditioner -- Your Ingenuity Required

I'm going to try using the readily available groundwater as my source for temperature regulation, run it through a heat exchanger and see how that works. I'll report back. Worst case is I've wasted maybe $500 to test the theory. Best case is I've permanently solved the problem for $500 and done it with as few moving parts as possible.

One mention on the dehumidification effect of running groundwater through a radiator. I have a pressurized water tank that is located in a sealed barn on this property, and condensation routinely forms on the tank during the summer when warm moist air hits the steel shell of the tank that is cool to the touch because it holds groundwater. I would assume condensation would likewise form on the heat exchanger if groundwater was pumped through it. This would have the effect of dehumidifying the air. That's my theory, anyway. I'll let you know if I'm correct.

SteveK

Re: Alternative Air Conditioner -- Your Ingenuity Required

Stoneunenged, good luck with the project. I'll be interested in what you come up with.

Blackcherry, the Mitsubishi H2i's bottom out at -13F. They can produce full rated BTU's at 5F and from there they drop off in capacity till -13F where they stop. Since I've never seen anything below -5F here, and we have a coal stoker to supplement if needed, we are pretty safe using this system. Mitsubishi has a new one out in Japan that will go -18F and run at more moderate temperatures at COP 5.0.

Blackcherry04

Re: Alternative Air Conditioner -- Your Ingenuity Required

SteveK wrote: »

Stoneunenged, good luck with the project. I'll be interested in what you come up with.

Blackcherry, the Mitsubishi H2i's bottom out at -13F. They can produce full rated BTU's at 5F and from there they drop off in capacity till -13F where they stop. Since I've never seen anything below -5F here, and we have a coal stoker to supplement if needed, we are pretty safe using this system. Mitsubishi has a new one out in Japan that will go -18F and run at more moderate temperatures at COP 5.0.

Could you explain what " Rated " output is ?? Is that taking a 36,000 BTU unit and downgrading it to say 16,000 BTU's . Do you still use 50-55 BTU's per SQ foot in temperature zone 5 ?? Are some of these figures that are posted mixing Fahrenheit and Celsius??

techntrek

Re: Alternative Air Conditioner -- Your Ingenuity Required

Shadowcatcher wrote: »

Geothermal heat pumps work quite well and are more efficient than an air to air even when ground water temp is not low enough to just run through a cooling coil. The question is what is the ground water temperature one source http://www.enoscientific.com/groundwater-temp-map.htm

The 26 SEER mini-splits are on-par with ground-source heat pumps right now, although when the ground-source heat pump industry begins to make inverter-based models then the balance will be tipped their way. They can't go too much farther though, I think max projected efficiency is in the low-30's SEER.

techntrek

Re: Alternative Air Conditioner -- Your Ingenuity Required

Blackcherry04 wrote: »

Could you explain what " Rated " output is ?? Is that taking a 36,000 BTU unit and downgrading it to say 16,000 BTU's . Do you still use 50-55 BTU's per SQ foot in temperature zone 5 ?? Are some of these figures that are posted mixing Fahrenheit and Celsius??

Directly from Mitsubishi's press release in 2009:

"For example, at 5 degrees Fahrenheit outdoors, systems can deliver 100 percent capacity. And at minus 13 degrees Fahrenheit, the P-Series H2i system can operate at 75 percent of rated heating capacity and the M-Series at 62 percent."

http://www.mitsubishipro.com/about-mitsubishi-electric/press-room/press-releases/mr-slim®-provide-unmatched-year-round-comfort

Here is a sales brochure, see page 2. It confirms 100% output of the 9000 BTU unit at 5 degrees Fahrenheit.

http://catalog.mitsubishipro.com/Asset/M-Series-Features-and-Benefits_new.pdf