How do you know if your geothermal system is performing to specification?
(continued from last month) Last month we talked about conducting a performance check on the water side of the geothermal water to air system…this month I want to continue but now let’s take a look at the refrigeration side of things.
We will again use the Comfort-Aire model HTV036 1200 CFM / FULL LOAD as our example.
Here’s what we know:
The Entering Water Temperature (EWT) is 60 degrees
The Leaving Water Temperature (LWT) is 52 degrees
This makes our water temperature drop 8 degrees
The Entering Water Pressure (EWP) is 51 PSI
The Leaving Water Pressure (LWP) is 46 PSI
The Entering Air Temperature (EAT) is 70 degrees
The Leaving Air Temperature (LAT) is 105 degrees
This makes our air temperature rise 35 degrees (105 – 70 = 35)
The Gallons Per Minute (GPM) is 9
We reviewed how to determine the GPM in the April 2012 newsletter so refer to it for a refresher if you need to.
The suction pressure is 120 PSIG
The suction line temperature is 53 degrees
The discharge pressure is 360 PSIG
The liquid line just prior to the expansion valve is 89 degrees
We will need to refer to a refrigerant temperature and pressure chart. You can see one at this address:
We can find the suction pressure of 120 PSIG at the far right vertical column which represents R410A refrigerant, (120 PSIG falls between 118 and 122.8 on the chart). We move left horizontally on the chart to the first vertical column and we see the corresponding temperature is about 41 degrees…this is our suction saturation temperature (SAT).
We can now calculate our superheat by simply subtracting the SAT (41 degrees) from the suction line temperature (53 degrees). 53 – 41 = 12 degrees superheat
This is good…we are making progress!
Okay…now let’s determine the subcooling. We will use the same refrigerant temperature and pressure chart and now find the discharge pressure (360 PSIG) on the far right column. We see that 360 falls between 355 and 365. We move left horizontally on the chart to the first vertical column and we see the corresponding temperature is about 109 degrees…this is our discharge saturation temperature (SAT).
We can now calculate our subcooling by simply subtracting the SAT (109 degrees) from the liquid line temperature (89 degrees). 109 – 89 = 20 degrees subcooling
Let’s assemble all the info we have collected so we can evaluate the refrigeration side of the system:
EWT = 60
GPM = 9 (the HTV036 is a 3 tom unit so the GPM is 3 / ton)
Suction Pressure = 120 PSIG
Discharge Pressure = 360 PSIG
Superheat = 12
Subcooling = 20
Water Temperature Drop = 8
Air Temperature Rise = 35
Now you need to refer to the products Unit Operating Conditions chart. You can find this chart in the HTV I & O manual on page 41 at this address:
We find the EWT on the far left of the chart…now you will see that the chart jumps from
50 – 70 degree EWT and our system has an EWT of 60. You need to ‘round-down’ and use 50 degree EWT on the chart. We know our GPM is 3 /ton so find 3 in the very next column to the right. Now we move horizontally to the right under ‘Full Load Heating’ to begin our performance check.
The first vertical column under Full Load Heating is Suction Pressure PSIG. The typical operating pressure for the HTV036 is 105 – 115 PSIG. The actual system operating suction pressure is 120 PSIG…which is HIGH!
The next vertical column moving to the right on the chart is Discharge Pressure PSIG. The typical operating discharge pressure for the HTV036 is 331 – 351 PSIG. The actual system operating discharge pressure is 360…which is HIGH!
The next vertical column moving to the right on the chart is Superheat. The typical operating superheat for a HTV036 is 10 – 15 degrees. The actual system operating superheat is 12 degrees…this is fine.
The next vertical column moving to the right on the chart is Subcooling. The typical operating subcooling for an HTV036 is 17 – 22 degrees. The actual system operating subcooling is 20 degrees…this is fine.
The next vertical column moving to the right on the chart is Water Temperature Drop. The typical operating water temperature drop for a HTV036 is 6.4 – 8.4. The actual system operating water temperature drop is 8 degrees…which is fine.
The last vertical column moving right on the chart is Air Temperature Rise. The typical operating air temperature rise for an HTV036 is 24 – 30 degrees. The actual system operating air temperature rise is 35 degrees…this is HIGH!
We have determined that the system is operating with HIGH suction pressure, discharge pressure and air temperature rise…chances are good we are over-charged!
So, between this month and the April 2012 newsletters we have seen how we can check both the water side and the refrigerant side of an operating geothermal water to air heat pump system. These checks are critical to establishing a proper operating system that will perform as intended and provide efficient heating and cooling for decades.
The HydroClaw by Storm King Enterprises
A couple buddies of mine have invented a new way to secure and safely mount a traditional diaphragm expansion tank on any structural member within the boiler room and / or on unistrut. The HydroClaw is the invention of Bruce and Jeff Perry, brothers from my home town in Orange County, NY. They were taught well by their dad, Mr. Don Perry, and there has been a Perry taking care of the community’s plumbing, heating and cooling needs since 1927.
You can tell how smart these guys are because they don’t work together…that seems to be a curse in our industry. I have seen too many family businesses ruined by feuding siblings. Bruce is the president / owner at Perry Plumbing, Heating & Cooling in Cornwall, NY and Jeff is the president / owner of Piedmont Radiant out of Charlottesville, VA.
These guys are not your average HVAC and plumbing contractors…each hold a college degree and each have talents and interests outside their ‘day jobs’.
The HydroClaw is truly a product born from ‘necessity being the mother of invention’. Bruce and Jeff are advocates of the new condensing boiler technologies where boilers have been taken off the floor where they were traditionally installed and now they are mounted on walls. Many of these boilers do not have integral expansion tanks and traditional air scoops for air removal have been replaced with low loss headers with integrated air removal devices. The problem the brothers faced…and I suspect many of us ‘wet heads’ do as well…is where and how to mount the diaphragm expansion tank?
The HydroClaw is an innovative and creative answer to this question…it securely grabs the tank within a steel clamp designed to mount to any structural member, (possibly right on the same wall the boiler is mounted), or to a piece of unistrut secured to structure. The HydroClaw is currently available in a size that accepts both #30 and #60 standard diaphragm expansion tanks of virtually all manufacturers as well as the ‘thermal’ type tanks for water heaters. The HydroClaw Jr. is soon to be released and it is designed to hold the smaller #15 tanks.
I think it is safe to say we all have unknowingly unthreaded what was a water-logged diaphragm expansion tank only to have it drop to the floor like a bowling ball because of the weight of the water…and if it hit your foot it was an experience you won’t long forget! A water-logged expansion tank creates a hazard of pipe breakage due to the excessive weight. The HydroClaw can prevent catastrophic damage resulting from a flooded expansion tank taking pipe and other system components with it as it tears from the system if not supported properly.
Now, before you suggest that Bruce and Jeff go on the show, ‘Shark Tank’, I have already suggested it and I wasn’t the first. I think the boys got something here that might, in time, even go beyond its initial intended use. I can see the HydroClaw being used to mount virtually any tank of any type… I also see a future for it as a seismic mount for water heaters and alike in areas prone to earthquake. You guys hear that in California?
I have posted two videos that the brothers have produced touting the advantages of the HydroClaw and how to install it properly. The videos can be seen under the tab ‘videos’. I have to tell you, I’m not only impressed with the HydroClaw itself but I think Jeff Perry has a future in ‘infomercials’…he is great in these videos and represents the product, himself and his brother very well.
The HydroClaw is patent pending and the boys are researching how best to bring the HydroClaw to the masses but for now you can buy directly from them at Storm King Enterprises. Call Bruce at 845-534-4270.
I had a chance to meet with a HVAC legend last week!
I conducted a Comfort Aire mini split cooling & heating class at FW Webb in Warwick, RI last Thursday. Charles Bursey is an Account Manager out of the Warwick location and he has been writing for the Fuel Oil News for decades. I was thrilled to meet Charles while I was there and to have him attend my class was very special indeed.
Charles has been an HVAC educator, author, advocate and icon for most of his life and he is an inspiration to guys like me who can only hope to establish a substantial, loyal following like Charles has over his career.
You can read Charles’ monthly column in the Fuel Oil News online at www.fueloilnews.com.
Go to the ‘columnists’ tab and click on Charles’ name to see all his current and archived articles…good stuff!
See you all soon!