Heat Pump TXV with 80 Degree Evaporator?

marx290 · 03-22-13, 08:37 PM

Ok, so I've never sized a thermostatic expansion valve for system, but I know how important it is to select the right one. Too small and the evaporator might starve, too large and it hunts to feed the appropriate amount of refrigerant. Other things like whether the TXV is internally or externally equalized, the type and placement of the sensing bulb, the pressure drop across the orifice, the evaporator itself, the type of refrigerant, so on and so forth. There are charts and engineering tables to help select the right valve and of course the knowledge and experience of seasoned technicians to go on.

The system I have in mind isn't really specific, but the general idea is a greywater sourced heat pump water heater. So, as far as the capacity of the system, compressor size and even the refrigerant used aren't really important to my question.

If a heat pump designed to recover heat from 100 degree F drain water and supply it to fresh, clean water at 120 degrees F; is there a thermostatic expansion valve capable of regulating superheat in an evaporator with a operating temperature range of 60-90 degrees F?

I'm wondering if TXVs designed for air to air or ground source heat pumps be able to properly feed and evaporator at those temperatures. Would a TXV work properly with a smaller pressure drop between the condensing pressure and suction? Are their any applications for a valve like this that there would exist sizing tables in this range?

This isn't something I'm planning on building anytime soon, just daydreaming.

jeff5may · 03-24-13, 02:10 AM

I believe what you are describing is known as a subcooling valve. It works the opposite way a normal TXV does. When the temperature is high, or temps are very close on both sides of the compressor, head pressure controls do a better job than suction pressure controls.

A Txv-metered system basically regulates the amount of liquid in the evaporator by maintaining constant superheat. When the system is started, the txv begins to open at a set pressure. As the evaporator temp drops, the txv responds by choking the flow to pull more heat out. This operation continues down to the lower limit of the valve. Below its limit, the valve acts on spring pressure, just like at start-up.

With subcooling valve controlled systems, the valve controls the amount of liquid in the condenser by maintaining constant subcooling. The evaporator is flooded, and maintains zero superheat. Mikesolar is in the process of building one of these, based on the design of a Westinghouse Hi-re-li heat pump from the 60's. Westinghouse was later bought by York, and sold the rights to this design to Paul Mueller. Mueller continues to make these units today, still based on the HiReLi design of 50 years ago. They renamed it the HiPerform and claim it to be the most energy efficient system in the world.

jeff5may · 03-24-13, 02:48 AM

Here's a brochure on the HiPerform unit, made for a flooded barrel chiller:
http://www.muel.com/pdfs/Literature/...rHiPerForm.pdf
A Sporlan Tech brief describing the problem you speak of:
http://sporlanonline.com/literature/90/90-198.pdf
Instead of using a subcooling valve, the sporlan guys do things the engineer way and the resulting kludge needs lots of controls to work.

Mikesolar · 03-24-13, 06:32 AM

The problem with Mueller is that they bought it for their own use and not to resell, AFAIK. The guy I work with had an old relationship with the Sporlan guys and managed to secure some. I don't know if he can still get them but the last time he had to buy 100 or something.

jeff5may · 03-24-13, 10:33 AM

After browsing the mueller website, I am convinced I would never be able to afford one of their units unless it was found in the scrap yard. High performance, high end industrial/commercial stuff aimed at bulk processing. Think dairy, fine wine/beer, big pharma, biotech. Set it and forget it stuff that don't break down. Brewmaster Bill has more important priorities than saving money on his wort chiller. Think Jurassic Park.

marx290 · 03-24-13, 12:36 PM

That's kind of what I was afraid of. From what I read, TXVs are a really great way to regulate superheat in an evaporator, keep it in a flooded state and ensure high vapor density back to the compressor. But, there is that pesky issue of a minimum pressure drop across the valve to supply sufficient refrigerant for the cooling needs.

I read that Sporlan article on controlling head pressure to keep steady TXV operation. Maintaining a minimum condenser pressure needed for proper TXV operation is quite necessary, I'm sure; and partially flooding the condenser to do it is genius, I think. Much better and more consistent than cycling a fan or pump. What alarms me, is the intentional adulteration of one part of a system as a response to the limits of another.

I'm not an engineer, and it would probably be different if I were made responsible for improving the performance or reduce power consumption of these systems. I won't say much more about the TXV. It can be an extraordinarily good at flooding a dry type evaporator if it is selected right.

What does anybody know about Gravity Flooded Evaporators with Low Side Float?

jeff5may · 03-24-13, 07:52 PM

I found a source for the mystery valve in question!

Hamby Dairy Supply :: Milk Cooling Tanks, Plate Coolers & FreeHeaters :: Replacement Parts for Milk Tanks :: Mueller :: Refrigeration components, temperature controls & sensors :: SubCool Valve 3 HP OH HIPERFORM

Not super cheap like txv's on ebay, but still within tinkering budget. I will be test driving one of these in the not too distant future.

Mikesolar · 03-25-13, 04:59 AM

Well, hit me on the head and call me shorty.........ya found one. Let the games begin.

jdrimm · 04-09-13, 02:31 PM

Mueller is a big name in dairy equipment, you might try farm auctions or even asking the local extension office about dairy farms that have ceased operations. Local dairy equipment suppliers might have bad chillers hanging around, too.

NiHaoMike · 04-09-13, 08:22 PM

Quote:

Originally Posted by marx290

That's kind of what I was afraid of. From what I read, TXVs are a really great way to regulate superheat in an evaporator, keep it in a flooded state and ensure high vapor density back to the compressor. But, there is that pesky issue of a minimum pressure drop across the valve to supply sufficient refrigerant for the cooling needs.

Use an orifice a step larger (such as a 1.5 ton one for a 1 ton system) and it will flow more. But it then might not operate properly at high condensing temperature. Another possible solution is to have a cap tube in parallel with the TXV, switched in with a solenoid valve on the low side

03-22-13, 08:37 PM	#1
marx290 Vapor Compression Goon Join Date: Mar 2013 Location: Portland, OR Posts: 63 Thanks: 11 Thanked 22 Times in 11 Posts	Heat Pump TXV with 80 Degree Evaporator? Ok, so I've never sized a thermostatic expansion valve for system, but I know how important it is to select the right one. Too small and the evaporator might starve, too large and it hunts to feed the appropriate amount of refrigerant. Other things like whether the TXV is internally or externally equalized, the type and placement of the sensing bulb, the pressure drop across the orifice, the evaporator itself, the type of refrigerant, so on and so forth. There are charts and engineering tables to help select the right valve and of course the knowledge and experience of seasoned technicians to go on. The system I have in mind isn't really specific, but the general idea is a greywater sourced heat pump water heater. So, as far as the capacity of the system, compressor size and even the refrigerant used aren't really important to my question. If a heat pump designed to recover heat from 100 degree F drain water and supply it to fresh, clean water at 120 degrees F; is there a thermostatic expansion valve capable of regulating superheat in an evaporator with a operating temperature range of 60-90 degrees F? I'm wondering if TXVs designed for air to air or ground source heat pumps be able to properly feed and evaporator at those temperatures. Would a TXV work properly with a smaller pressure drop between the condensing pressure and suction? Are their any applications for a valve like this that there would exist sizing tables in this range? This isn't something I'm planning on building anytime soon, just daydreaming. __________________ To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

03-24-13, 02:10 AM	#2
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	I believe what you are describing is known as a subcooling valve. It works the opposite way a normal TXV does. When the temperature is high, or temps are very close on both sides of the compressor, head pressure controls do a better job than suction pressure controls. A Txv-metered system basically regulates the amount of liquid in the evaporator by maintaining constant superheat. When the system is started, the txv begins to open at a set pressure. As the evaporator temp drops, the txv responds by choking the flow to pull more heat out. This operation continues down to the lower limit of the valve. Below its limit, the valve acts on spring pressure, just like at start-up. With subcooling valve controlled systems, the valve controls the amount of liquid in the condenser by maintaining constant subcooling. The evaporator is flooded, and maintains zero superheat. Mikesolar is in the process of building one of these, based on the design of a Westinghouse Hi-re-li heat pump from the 60's. Westinghouse was later bought by York, and sold the rights to this design to Paul Mueller. Mueller continues to make these units today, still based on the HiReLi design of 50 years ago. They renamed it the HiPerform and claim it to be the most energy efficient system in the world. Last edited by jeff5may; 03-24-13 at 02:18 AM..

03-24-13, 12:36 PM	#6
marx290 Vapor Compression Goon Join Date: Mar 2013 Location: Portland, OR Posts: 63 Thanks: 11 Thanked 22 Times in 11 Posts	Flooded Evaporator - Low Side Float That's kind of what I was afraid of. From what I read, TXVs are a really great way to regulate superheat in an evaporator, keep it in a flooded state and ensure high vapor density back to the compressor. But, there is that pesky issue of a minimum pressure drop across the valve to supply sufficient refrigerant for the cooling needs. I read that Sporlan article on controlling head pressure to keep steady TXV operation. Maintaining a minimum condenser pressure needed for proper TXV operation is quite necessary, I'm sure; and partially flooding the condenser to do it is genius, I think. Much better and more consistent than cycling a fan or pump. What alarms me, is the intentional adulteration of one part of a system as a response to the limits of another. I'm not an engineer, and it would probably be different if I were made responsible for improving the performance or reduce power consumption of these systems. I won't say much more about the TXV. It can be an extraordinarily good at flooding a dry type evaporator if it is selected right. What does anybody know about Gravity Flooded Evaporators with Low Side Float? __________________ To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

03-24-13, 02:48 AM	#3
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Here's a brochure on the HiPerform unit, made for a flooded barrel chiller: http://www.muel.com/pdfs/Literature/...rHiPerForm.pdf A Sporlan Tech brief describing the problem you speak of: http://sporlanonline.com/literature/90/90-198.pdf Instead of using a subcooling valve, the sporlan guys do things the engineer way and the resulting kludge needs lots of controls to work.

03-24-13, 06:32 AM	#4
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	The problem with Mueller is that they bought it for their own use and not to resell, AFAIK. The guy I work with had an old relationship with the Sporlan guys and managed to secure some. I don't know if he can still get them but the last time he had to buy 100 or something.

03-24-13, 10:33 AM	#5
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	After browsing the mueller website, I am convinced I would never be able to afford one of their units unless it was found in the scrap yard. High performance, high end industrial/commercial stuff aimed at bulk processing. Think dairy, fine wine/beer, big pharma, biotech. Set it and forget it stuff that don't break down. Brewmaster Bill has more important priorities than saving money on his wort chiller. Think Jurassic Park.

03-24-13, 07:52 PM	#7
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	I found a source for the mystery valve in question! Hamby Dairy Supply :: Milk Cooling Tanks, Plate Coolers & FreeHeaters :: Replacement Parts for Milk Tanks :: Mueller :: Refrigeration components, temperature controls & sensors :: SubCool Valve 3 HP OH HIPERFORM Not super cheap like txv's on ebay, but still within tinkering budget. I will be test driving one of these in the not too distant future.

03-25-13, 04:59 AM	#8
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	Well, hit me on the head and call me shorty.........ya found one. Let the games begin.

04-09-13, 02:31 PM	#9
jdrimm Lurking Renovator Join Date: Apr 2013 Location: KY, USA (deployed to Djibouti, Africa) Posts: 8 Thanks: 3 Thanked 0 Times in 0 Posts	Mueller is a big name in dairy equipment, you might try farm auctions or even asking the local extension office about dairy farms that have ceased operations. Local dairy equipment suppliers might have bad chillers hanging around, too.