I'd normally go directly to my geo contractor about this, but figured I'd post it here in case someone else had the same question. I just got my geo w2w system running. Previously, I was running a boiler system which had a taco radiant mixing block(rmb) located right before my zones. My rmb was used for a few things. 1) outdoor reset 2) prevented my boiler from condensation 3) mixed my exiting water temp from my zones with the boiler water to mix at a designed water temp. Example: boiler temp =150 deg, exiting zone temp= 100, desired mixing temp =120. I noticed last night that when trying to send 100 deg into the loop, when my exiting zone water was mixed with the buffer tank temp (100 deg), my entering loop temp would be reduced to 91-95 deg. My concern is now that I'm no longer mixing with such a high water temp, unless I increase my buffer tank temp, I'll never send the desired temp into my loops. My solution ,if needed would be to remove my rmb and install a circulating pump. Now my real question is whether it's more efficient to use 1 circulating pump for all zones, or is it better to have a smaller circ pump for each zone? Keep in mind my geo is still bringing the house up to temp, so I still have to see how the rmb performs once I'm at desired temp.
Depends. Often existing wiring, plumbing will dictate the likeliest solution. You may consider a delta P or T pump. They can serve multiple zones quite effectively. You do need to start out knowing your flows and headloss for the zones. To size whatever pump(s) you require.
The Taco RMB-1 should be removed from the system. The documentation says the "Boiler" supply temp should be 20f higher than the radiant loop temp. Geo system supply should not be mixed down or you will be paying the premium of lost COP at higher temperatures. http://www.taco-hvac.com/uploads/FileLibrary/102-151.pdf Please consider controlling the buffer tank temp and W2W HP with outdoor reset to maximize efficiencies available at lower temperatures. If you can swing it, the most efficient option would be a properly sized variable speed pump and zone valves to feed your radiant .
Thx for the replies. I assumed I would be removing it, but I figured I'd check to see what others said. I've switched my rmb to manual (less mixing) until I can get it replaced. I have zone valves for each zone, just need to size a speed pump and get an outdoor reset. Thx again for the replies.
Anyone know a good site to calculate head loss? My hydronic heating book takes me all over the place and doesn't describe it as well as I need. Some say I'm"simple". Edit: Maybe I should add a bit more here. Here's what I'm assuming so far using the chart below. http://www.uponorpro.com/~/media/Extranet/Files/manuals/PressureLossTables_H191_1210.aspx?sc_lang=en If I'm using 3/4 pex, 100% water at 100 deg. And I've calculated my gpm to be .37 per loop (3 loops ~250 ft) My pressure loss per 100 ft would be around .16. .16 x 2.5 = .4 .4 x 3(loops)= 1.2 ft head .37 gpm x3(loops) = 1.11 gpm for zone. So I would be looking for a pump that pushes 1.11 gpm at 1.2 ft head? How do I take my other loops into consideration?
Check out climatemasters website. I found a nice pdf on how to calculate head loss. Has charts ect.... Don't forget to add in the gshp's exchangers loss. Also here. I have not had time to use it myself yet but looks like a nice tool. http://www.climatemaster.com/geothermal-dealer/geothermal-sales-tools/pressure-drop-calculator/
headtohome, if it came from climatemaster, it is likely more focused on source side side plumbing. OP is concerned about the load side. But, I'm on a remote, so can't open it to verify.
Taco has a good source for sizing circulators if you don't mind calculating by hand. No matter which brand the math is all the same. http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf Doing it by hand forces you "think" about all the components your piping system. A couple tips- -Consider using a DeltaT of 10f or less for geo when determining total GPM. This will help lower supply temps for efficiency. -The head has to be added up for every component in series. -For loops in parallel only add the head of the loop with the highest head calculated with target individual loop flow rate. All this means nothing if you do not have a heat loss calculation to target your load.
Headoldhome, I'll have to wait till I get a chance to get to a computer to look at your link, but looks like it could be useful down the road. Geoxne, great site. I usually tend to do hand written calcs myself as well. Question on the calculations though. The example used was 1 zone at 100,000 BTU's. Do I use my total house BTU's/hr but change my tubing type to 3/4 instead of the calculated type, or do I calculate each zone individually? If individually, do I add the total gpm and head loss at the end to determine my max, and use the lowest as my min?
I'm certainly not a expect on this topic (but I've been doing some homework in this area as I'm trying to decide what I want to do in my garage).... GPM - you add the numbers together for each loop to get the total GPM the circulator needs to move Head - since the loops are in parallel, the head pressure does not add. Just calculate the head pressure of one loop and this is the head pressure the circulator will see.
Alright, let me see if I can break this down as a simple example for myself. If I had three loops: Zone 1 - 3 loops, each loop calculated to be .33 gpm each loop 250 ft, 260 ft, 265 ft Zone 2 - 2 loops, each loop calculated to be .4 gpm. Each loop 150 ft , 180ft Zone 3 - 3 loops, each loop calculated to be .3 gpm. One loop 150ft, 175 ft, 300 ft Would I then add 3(.33)+2(.4)+3(.3) = 2.69 gpm Then take the longest loop 300 ft at 3/4" at say 100 deg. The head pressure would be .12? I still need to take my piping before and after the loops into consideration, but as Bill Murray says "baby steps"
You will look and look until you KNOW what the head loss is. Post pictures if you can of the near machine piping and any manifolds. I learned from the Wilo guys that every pump is over sized. Period. Even Wilo pumps. Do take a hard look at Taco, their Bumble Bee product looks very good. I have yet to use it. You will find stuff out there that have funny lines called pump curves. One takes the GPM and the loss of pressure in feet of Head and finds a point on a two dimensional graph. Then one takes that point to the pump curve chart and picks a pump that does more than the graph point. That is why pumps are always over sized. If you get stuck give me a call. Mark
A picture of your set up would surly help to see how the pex radiant loops split off into the different zones. Your GPM seem low to me... in the reading I've done, for 3/4" pex you want to keep your flow above 2.3 GPM so you don't end up with air bubbles getting trapped in the loop. Are you sure your flow numbers are correct? Or looking from another view.. Q = f * 500 * delta T Geo delta T should be around 10 Q = 2.69 * 500 * 10 Q = 13450 ... seems very low
This is my fault, I used fake numbers just for scenario purposes. Wanted to make sure my thinking process was correct. I'll take a picture tonight of my system with some real numbers. Mark, I was looking at the bumble bee as well. Just wanted to make sure I didn't undersize my pump before I purchased it. I agree that from what I've read is that most pumps are oversized. I assume this is why the variable speed is a plus? Thanks for all the replies. This is a great forum to learn from.
ok, using your phoney numbers we have: H = (.00731)(1.095)(300)(.3^1.75) = .29 Not sure how you got .12 (oh, it looks like .12 is just .3^1.75... I think you may need to hit the = key again on the calculator to get the 'final' result)
Hi Ben, Hadn't noticed this here. I commented once about this site being over compartmentalized. Anyway based on yesterdays conversation it sounds like we are dialing in.
