EcoRenovator  

Go Back   EcoRenovator > Improvements > Appliances & Gadgets
Advanced Search
 


Blog 60+ Home Energy Saving Tips Recent Posts Search Today's Posts Mark Forums Read


Reply
 
Thread Tools Display Modes
Old 03-27-10, 09:24 AM   #1
NiHaoMike
Supreme EcoRenovator
 
NiHaoMike's Avatar
 
Join Date: Oct 2008
Location: Austin, TX
Posts: 1,154
Thanks: 14
Thanked 257 Times in 241 Posts
Default Interesting compressor for solar refrigeration and mini A/C

Thermaltake Xpressar - World's First DC Inverter Type Micro Refrigeration Cooling System
Quote:
1. How much power the compressor consumes?

Ans. The compressor consumes 50 watts maximum.

3. What kind of refrigerant does Xpressar™ RCS100 use?

Ans. The Xpressar™ RCS100 uses R134a refrigerant, it is industry standard and widely used in vehicles & household conditioning.

5. What kind of power connector does Xpressar™ RCS100 use?

Ans. The Xpressar™ RCS100’s input is DC 12V.

__________________
To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
NiHaoMike is offline   Reply With Quote
Old 03-27-10, 02:32 PM   #2
Ryland
Master EcoRenovator
 
Join Date: Mar 2009
Location: Western Wisconsin.
Posts: 913
Thanks: 127
Thanked 82 Times in 71 Posts
Default

sure it only draws 50 watts... but for that energy use how much does it cool? if I remember correctly my fridge only draws around 150-180 watts while it is running.
Ryland is offline   Reply With Quote
Old 03-27-10, 07:43 PM   #3
NiHaoMike
Supreme EcoRenovator
 
NiHaoMike's Avatar
 
Join Date: Oct 2008
Location: Austin, TX
Posts: 1,154
Thanks: 14
Thanked 257 Times in 241 Posts
Default

A CPU used in such a system dissipates a lot of heat. Maybe about 100-150w overclocked.

I think it would work very well for a mini solar A/C intended to be used on the days when even a powerful fan isn't quite enough.
__________________
To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
NiHaoMike is offline   Reply With Quote
Old 03-28-10, 02:21 AM   #4
Piwoslaw
Super Moderator
 
Piwoslaw's Avatar
 
Join Date: May 2009
Location: Warsaw, Poland
Posts: 960
Thanks: 188
Thanked 110 Times in 86 Posts
Default

I've seen mini-fridges with a 55W compressor, but they were AC. I don't know about the ones designed for automotive/RV use, they may be DC powered, or DC-inverter-AC (much less efficient.

A DC powered compressor is harder to find, but it does have its good sides. A few years back I remember reading in a solar magazine about a DC powered heat pump, designed for solar systems. If I find it, I'll update this post.

UPDATE: I found it in Solar Today, Jul/Aug 2001, p.51-52. The heat pump was SUNStation by Sun Utility Network, Inc., L.A. Cal. It appears that the company no longer exists, since googling "SUNStation" doesn't produce any results, and their page www.sunutility.com can't be found.
Googling for DC heat pumps shows that there are 12/24V A/c and split models for truck drivers. May be enough to help heat/cool one room.

Last edited by Piwoslaw; 03-28-10 at 12:48 PM..
Piwoslaw is offline   Reply With Quote
Old 03-28-10, 11:18 AM   #5
NiHaoMike
Supreme EcoRenovator
 
NiHaoMike's Avatar
 
Join Date: Oct 2008
Location: Austin, TX
Posts: 1,154
Thanks: 14
Thanked 257 Times in 241 Posts
Default

DC compressors are often called inverter drive compressors. In general, about the only difference from a regular compressor is that the stator is 3 phase since that is optimal for control purposes. (There are exceptions, such as the "Tesla Turbocompressor" prototype my friend is working on, which has a switched reluctance motor that runs as fast as 75kRPMs! It uses distilled water as a refrigerant due to the high flow rates and low operating pressures.) But in theory, it is possible to operate a regular compressor motor as a 2 phase motor.

Direct-to-line motors are difficult to optimize for efficiency under varying load conditions since the torque angle can never be optimized over a range of load torques. Inverter drive motors are therefore often more efficient. Then reductions in delta T in HVAC systems at partial capacity increase efficiency even further. In fact, it is possible to increase the efficiency of an A/C by downsizing the compressor, without changing the technology used.

How to Add or charge Freon or Refrigerant to your air conditioning equipment
Quote:
Simply put what makes one unit more efficient than another is bigger coils in relation to the compressor capacity. This is the dirty little secret that no one wants to talk about. Because if they did talk about it then it wouldn't be a secret.
...
Note: This 3 ton coil had a leak and was replaced in the late 90s. It has since been repaired and donated to a needy family along with a Carrier 5 ton outdoor coil (no compressor at the time) and a 2.5 ton Rotorex rotary compressor in a house that had a 4 ton gas air conditioner and all the surrounding houses have 4 or 5 ton systems, this one cools just fine. No wonder the other contractors hate me!
__________________
To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
NiHaoMike is offline   Reply With Quote
Old 03-28-10, 01:04 PM   #6
Piwoslaw
Super Moderator
 
Piwoslaw's Avatar
 
Join Date: May 2009
Location: Warsaw, Poland
Posts: 960
Thanks: 188
Thanked 110 Times in 86 Posts
Default

Mike, so are you saying that adding a larger heat exchanger (on one or both sides?) increases the efficiency of a heat pump?

I read that DC is better than AC for ventilation fans because it's easier to control speed, plus it almost eliminates noise (no humming or vibrations). I believe it was also slightly more efficient, but I'm not sure about that one. I guess that pumping air in a duct is not the same as compressing refrigerant, so just replacing the AC part with DC won't work?

I think the varying load problem is solved in new units by plumbing 2-3 smaller compressors in parallel, each one being turned on only when needed. This, and using a spiral compressor instead of the older piston style, supposedly greatly increases efficiency.
Piwoslaw is offline   Reply With Quote
Old 03-28-10, 04:07 PM   #7
NiHaoMike
Supreme EcoRenovator
 
NiHaoMike's Avatar
 
Join Date: Oct 2008
Location: Austin, TX
Posts: 1,154
Thanks: 14
Thanked 257 Times in 241 Posts
Default

Quote:
Mike, so are you saying that adding a larger heat exchanger (on one or both sides?) increases the efficiency of a heat pump?
Yes, it reduces the delta T the heat pump has to work with. But such high pressure heat exchangers are relatively expensive. Diminishing returns also becomes an issue very quickly.
Quote:
I read that DC is better than AC for ventilation fans because it's easier to control speed, plus it almost eliminates noise (no humming or vibrations). I believe it was also slightly more efficient, but I'm not sure about that one.
There is a very significant increase in efficiency, but most of it is not from the motor. Most of the savings is from reducing speed during part load conditions, since aerodynamic losses are exponential (or to some power, forgot which) to speed and duct pressure drops are roughly proportional to flow. Inverter drive motors can operate over a wide speed range instead of 3600RPMs and its submultiples like most direct-to-line motors.

I have a computer fan with an ECM (electronically commutated, same as inverter drive) motor. It is much more efficient than an AC desk fan of roughly the same size.
Quote:
I guess that pumping air in a duct is not the same as compressing refrigerant, so just replacing the AC part with DC won't work?
The load curves are very different, so the exact same method of control cannot be used. Valve losses in reciprocating compressors decreases with speed.
Quote:
I think the varying load problem is solved in new units by plumbing 2-3 smaller compressors in parallel, each one being turned on only when needed. This, and using a spiral compressor instead of the older piston style, supposedly greatly increases efficiency.
The main problem is that power electronics are cheap and compressors are expensive. So using power electronics is a more economical solution to the same problem. (The average compressor costs several hundred dollars while IGBTs at the power levels in HVAC are less than $2 each.)
HGT1S12N60A4S9A Fairchild Semiconductor IGBT Transistors
__________________
To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
NiHaoMike is offline   Reply With Quote
Old 04-28-10, 10:18 AM   #8
mrd
Apprentice EcoRenovator
 
Join Date: Feb 2010
Location: Milford, DE
Posts: 106
Thanks: 5
Thanked 9 Times in 9 Posts
Default

Quote:
Originally Posted by NiHaoMike View Post
Yes, it reduces the delta T the heat pump has to work with.
I think you mean the larger surface area requires a lower delta T to match the load at constant fan operation. So you want a smaller compressor to provide a lower delta T at an efficient operating cost. (Perhaps you could use a larger compressor with a different amount of refrigerant, but it wouldn't be efficient.. not sure)

Changing fan speed will change the rate of heat exchange, which will reduce efficiency of compressor-to-heat-exchanger-area combination. So, ideally when changing fan speed, you also change compressor rate or surface area (to maximize efficiency of meeting the load.)

However, there are other factors to system design. Humidity control is important to comfort and health. The indoor coil can provide dehumidification to keep levels below a maximum. Rate of dehumidification depends on coil area, temperature, and air flow.

Air speed at ducts affects temperature stratification and air distribution noise levels. Typically, your ductwork is sized to provide a certain exit velocity for a specific flow rate. Changing the fan speed throws off duct design, unless your ductwork contains active components to maintain exit velocities (very unlikely.)

So ideally the fan speed is constant, and compressor rate and surface area are variable. I'm not familiar with variable surface area systems, but I would guess a few rows of coils with electronic valves could work. The compressor rate and surface area change to meet the load at maximum efficiency, and to dehumidify at a desired rate. I suppose you could say, to meet the sensible and latent loads appropriately.. but I find it intuitive to clearly distinguish between latent load and total load.

Last edited by mrd; 04-28-10 at 10:30 AM..
mrd is offline   Reply With Quote
Old 04-28-10, 10:25 AM   #9
mrd
Apprentice EcoRenovator
 
Join Date: Feb 2010
Location: Milford, DE
Posts: 106
Thanks: 5
Thanked 9 Times in 9 Posts
Default

Quote:
Originally Posted by mrd View Post
Air speed at ducts affects temperature stratification and air distribution noise levels. Typically, your ductwork is sized to provide a certain exit velocity for a specific flow rate. Changing the fan speed throws off duct design, unless your ductwork contains active components to maintain exit velocities (very unlikely.)
Although, I might add, as the delta T of the tempering air to distributed air is reduced, meeting stratification expectations requires lower exit velocities. This equates to lower flow rates, which improves efficiency due to lower friction losses, as you mentioned earlier.

As such, the fan speed could be reduced with lower delta T to even further improve efficiency. Certainly there are algorithms to optimize all of these factors together to maximize efficiency while meeting the design requirements. It just requires all the components to work together, flexibly, and be designed properly.
mrd is offline   Reply With Quote
Old 04-29-10, 11:14 AM   #10
NiHaoMike
Supreme EcoRenovator
 
NiHaoMike's Avatar
 
Join Date: Oct 2008
Location: Austin, TX
Posts: 1,154
Thanks: 14
Thanked 257 Times in 241 Posts
Default

Quote:
Originally Posted by mrd View Post
However, there are other factors to system design. Humidity control is important to comfort and health. The indoor coil can provide dehumidification to keep levels below a maximum. Rate of dehumidification depends on coil area, temperature, and air flow.
Use a pair of heat exchangers around the evaporator to improve dehumidification. One way to make it is to use two car radiators and a bilge pump or fountain pump. If you want dehumidification, turn the pump on. The first radiator will precool the air, allowing for a lower evaporator temperature for better dehumidification. The second radiator will then reheat the air while cooling the coolant for the first radiator.

My friend is not planning for that feature in her design, since the areas where hybrid A/C works the most efficiently are the areas that are naturally low in humidity.

__________________
To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...
NiHaoMike is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 10:45 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Ad Management by RedTyger
Inactive Reminders By Icora Web Design