Oversized water coils and superheat

[hult]

Several manufacturers now advertise over-sized water coils, including for water-water units, as a feature that increases efficiency.

How is this done and still keep the superheat within the desired range? Or doesn't it matter with water coils?

[teeball57]

The industry as a whole has been increasing coil size on air and water alike to increase efficiency. The superheat is controlled by the TXV and system charge assuming proper flow rates.
Scrolls are the norm these days and somewhat forgiving in such matters.

[hult]

The industry as a whole has been increasing coil size on air and water alike to increase efficiency. The superheat is controlled by the TXV and system charge assuming proper flow rates.
Scrolls are the norm these days and somewhat forgiving in such matters.

"Somewhat forgiving" is one matter. It would seem to me that more than _doubling_ the water coil size as at least one geothermal manufacturer has done is quite another matter -- especially in the context of the incessant drumbeat 'out there' admonishing to not oversize air coils.

Question: Is increasing the system charge sufficient to allow the TXV to maintain desired superheat if one doubles up on coils (as one manufacturer does) keeping the compressor size the same?

[teeball57]

Question: Is increasing the system charge sufficient to allow the TXV to maintain desired superheat if one doubles up on coils (as one manufacturer does) keeping the compressor size the same

I think we need to keep this in perspective here.
In the case of a w to w unit we have 2 matched coils evaporator and condenser. If you increase the size of the coils and match the TXV, the gas charge would increase to accommodate the the extra liquid needed in the system. This is done in a lab environment to monitor the performance.
In a stand alone unit they can dial in the gas charge to the oz.

Not sure what you mean by "doubles up on coils". Do you have specifics?

[hult]

Question: Is increasing the system charge sufficient to allow the TXV to maintain desired superheat if one doubles up on coils (as one manufacturer does) keeping the compressor size the same?




I think we need to keep this in perspective here.
In the case of a w to w unit we have 2 matched coils evaporator and condenser. If you increase the size of the coils and match the TXV, the gas charge would increase to accommodate the the extra liquid needed in the system. This is done in a lab environment to monitor the performance.
In a stand alone unit they can dial in the gas charge to the oz.

So -- keeping it in perspective -- Is the/your answer "Yes" for standalone water-to-water units ? ;-)


Not sure what you mean by "doubles up on coils". Do you have specifics?

Here is a GSHP manufacturer using coils rated at 5 tons for 2-ton units and two 5-ton coils -- "doubled up" -- in a 5-ton unit.

http://www.geothermalheatpump.com/features.htm

Sunteq-Enviroteq shows a picture of its apparently proprietary (?) parallel configuration of two coils (which are actually six coils in parallel in two separate units).

Packless sells coils with manifolds that are two identical colis duplexed ("doubled up")

http://www.packless.com/catalog/ItemView.aspx?id=49

and quadruplexed ("quadrupled")

http://www.packless.com/catalog/ItemView.aspx?id=59 -- click on "More Images" and then "Next".

so this by itself is an industry standard, and not unusual.


Question: Is increasing the system charge sufficient to allow the TXV to maintain desired superheat if one doubles up on coils (as one manufacturer does) keeping the compressor size the same?

Is this question clearer now?

Other than 1) increasing amount of charge and assuring that 2) the TXV temperature sensor and 3) the TXV external connection are properly position on the manifold, what else would be needed for a manufacturer to offer a system with efficiency increased by "doubling up" ?

TIA ... Marc

[teeball57]

The Sunteq units use 2 compressors in a single refrigeration circuit. That idea has been abandoned by most all GEO manufactures for many reasons such as cost and size constraints. (not to mention service and reliability issues) So it would not be considered an industry norm.
The Packless coax is manifolded together on the water side for commercial units. An example would be a 10 ton unit would have 2 separate 5 ton refrigeration circuits or 2 stages of heat or cool. They manifold the water side so only one water connection to the unit is needed. Helps save space too.
The "double up" of the coax is not done for higher efficiency.

The size of the coax has increased over the years as has the condenser coil on the split air units to improve efficiency.

[hult]

The Sunteq units use 2 compressors in a single refrigeration circuit. That idea has been abandoned by most all GEO manufactures for many reasons such as cost and size constraints. (not to mention service and reliability issues) So it would not be considered an industry norm.

No one has stated in this thread that two compressors are the norm.

What Sunteq does unambiguously state at the url I sited is that they use (eg) five tons of coil for a two-ton unit a 2.5:1 ratio. This constitutes (more than) doubling the coil size over standard. And that they do this to increase efficiency. They state:

" " [T]he heat exchangers on Enviroteq's closed loop models are greatly oversized - 200% on average - for incredibly high heat extraction efficiency. " "


The Packless coax is manifolded together on the water side for commercial units. An example would be a 10 ton unit would have 2 separate 5 ton refrigeration circuits or 2 stages of heat or cool. They manifold the water side so only one water connection to the unit is needed. Helps save space too
The "double up" of the coax is not done for higher efficiency

Are you describing an application of a different coil than the ones I cited? They clearly have a single input and a single output for both water _and_ refrigerant. If refrigerant valving/connections are such that only one five-ton compressor is operating in a two-compressor, 10-ton system that always circulates refrigerant to all coils (re-view diagram of the coils I cited) , how is this not "doubling up" and why would not it not increase efficiency ?

But my reference was simply to point out the availabilty of actual parts from an actual principal standard coil suppplier that would actually allow a manufacturer to actually "double up" coils (both literally and quantitatively) without so much as actually making a single additional braze *if* the answer to my question is "Yes" -- For example, "doubling up" by using a Packless "duplexed" (2-coils + manifold ) 10-ton COAX-3010-S instead of a Packless 5-ton single coil COAX-2500-S.


The size of the coax has increased over the years as has the condenser coil on the split air units to improve efficiency

Yes. Understood. We've been here before. The question I asked that has not been answered is:

Other than 1) increasing amount of charge and assuring that 2) the TXV temperature sensor and 3) the TXV external connection are properly position on the manifold, what else would be needed for a manufacturer to offer a system with efficiency increased by "doubling up" ?


Thank you for your patience (and thanks in advance to others who may still also reply ) ... Marc

[teeball57]

The heat exchangers on Enviroteq's closed loop models are greatly oversized - 200% on average - for incredibly high heat extraction efficiency.

The problem here is a see no numbers backing this claim.
Most manufacturers back their claims with spec sheets showing EER & COP.
I found no such information on that site.

As I have been told "without data you only have opinion".

[hult]

The heat exchangers on Enviroteq's closed loop models are greatly oversized - 200% on average - for incredibly high heat extraction efficiency.

The problem here is a see no numbers backing this claim.
Most manufacturers back their claims with spec sheets showing EER & COP.
I found no such information on that site.

As I have been told "without data you only have opinion".

But you have stated/repeated:



The size of the coax has increased over the years as has the condenser coil on the split air units to improve efficiency



The industry as a whole has been increasing coil size on air and water alike to increase efficiency.

So strking the word "incredibly" from Sunteq's assertion and you would appear to be in complete agreement. Even we include the descriptive term "incredibly" and so consider the phrase in its entity, yours would be only a qualitative difference of opinion, not of quantitatively different facts.

The question I posed that remains unanswered while we circle 'round and 'round is:


Other than 1) increasing amount of charge and assuring that 2) the TXV temperature sensor and 3) the TXV external connection are properly position on the manifold, what else would be needed for a manufacturer to offer a system with efficiency increased by "doubling up" ?


Paraphrasing Daniel Patrick Moynihan: "We are entitled to our own opinions, but not our own facts" .

... Marc Hult hult@hydrologist.com

[teeball57]

Ahh , but we have no proof that "doubling up" an already larger coax will increase the efficiency. Do you suppose the larger GEO manufacturers have given that any thought. After all they spend a lot of time and money squeezing every bit of efficiency they can out of design.