checking ewt/lwt

What is the most accurate way to check ewt/lwt on a closed loop system with no p/t ports?
Should I tape a digital thermometer to the inlet/outlet loops or directly to the brass elbows on the heat pump?
This is a 5 ton climate master with 5 loops 200'x1.25" hooked up in series and installed back in 2007.

 

After making comments about the original installer, I would take it off the brass fittings as close to the heat pump connections as possible. Use insulation. And, if using two thermometers, I would ensure the both read the same temperature on one side first (for calibration).

Hooked up in series?

 

Outside Temp is 40 deg.
Set point of 70 Deg.

Taped to the outside of 1.25" poly under insulation:
EWT 48.7
LWT 41.8

Single tank Desuperheater set up.
Upgrading to a buffer tank.

 

Dan:

The operation of, and measuring of what goes on with a geothermal system is a moving target. As you move towards steady state operation things start to change. You extend your call for heat so that you can get your test numbers and, in heating you chill the loop.

Metal is faster than plastic for heat conduction, so if I have a fast window to measure without distorting the building's real needs I go with thermistors on the copper just inside the cabinet. A razor knife cut in the insulation and hard contact with the piping is fast. The wound is easily sealed with electrical tape.

The 6.9*F delta T you are seeing is well within CM standards at those water temps in heating.

Now why do you ask?

Getting into service or checking your own work?

Mark

 

I am not getting into service, that's left for the professionals in that field! I was just looking at my fathers geothermal system we installed in 2007. It was our first closed loop we designed and installed ourselves. It has never failed or given us any problems at all. Just curious as to how well or not well it was performing after 5 years. We are going to be installing a buffer tank to help the desuperheater perform better. We worked with another first time installer, who we have grown with and done many jobs with over the years now. Just curious, and it seems to be working fairly well performance wise. It was our one and only system we installed "in series". I personally believe its a good idea for small loop fields.

 

so you have the vertical loops piped in series????

 

That is correct.
5 loops all 1.25" x200' each. Tied together end to end. Making one single circuit 1.25"x1000' long. It's been 5 yrs, and no issues.
Im sure some one will ask soon, so it's a u26-99u twin pump flow center.

Its at my fathers house , so if some reason it failed or was too much for pumps we could re connect it in a reverse return. So far so good.

 

Sure, will work borderline, giving you about 12 gpm of flow at a system pressure drop of 52 ft/hd. If you would have done 2 circuits you pressure drop would have been 22 ft/hd and you would have gotten 13 gpm with a single 26-99, savings you about 50% of the circulation costs/power. Plus 100ft/ton of borehole is kind of short, so either you are running your loop pretty cold, or you temps are OK but then your 5 ton units is oversized. Either way it is not optimal.

 

Typo....
that is 200' borehole each. Making 1.25"x2000' long circuit.

 

Autsch...2000 ft of pipe give you 87 ft/hd of pressure drop and only 9.75 gpm of flow with (2) 26-99 pumps, very low for a 5 ton heat pump. So now you are paying twice as much for circulation power then you would need, and still have a poorly performing heatpump because you are not feeding it with enough water flow. (4) boreholes with 125 depth and (4) 500 ft 1.25" pipes would have given you 14 gpm with a single 26-99.

 

At your specs this would be completely short looped. 4 bores@ 125 each? Your talking about 100' per ton. Way too short.
i agree with the pumping consumption being more than it would be if they were tied in parallel.
And your talking about just shy of 2 gpm/ton, which is not too alarming either.

 

Typo....I meant your 2000 ft of pipe broken out at 4 circuits of 500', with 250' bores. That would give you 14 gpm with (1) 26-99. Reynolds number is around 2000, you could use 1" pipe and you get around 2500 with 13 gpm flow. Getting below 2 gpm/ton would concern me a bit, it depends on how cold your loop runs at the end of the heating season.

 

Well this simple question snowballed into a debate over what designs would produce higher flow rates, or the ability to use less power for pumping the loops. Either way it doesn't matter much right now.
all I was asking for is a simple way to check loop temps to see how it has been performing.
I will be putting new elbows with p/t ports when we redo the dsh setup.

 

Sorry, but you were the one who posted your design here, and to push the entire flow needed by the heatpump through a single pipe is not a very efficient way, at least not if you need between 12-15 gpm and your pipe is 2000 ft long. Your were lucky that your system works (although not very efficiently), we have many examples here where they were installed in a similar fashion and don't work, to the detriment of the homeowner.
They are a lot of DIYs here, or inexperienced contractors, and your comment here that this kind of design is "a good idea" for smaller loops is simply misleading. It is not a good idea. You own systm has over 80 ft/hd. A well designed loop should have a high flow rate AND the lowest possible pumping power.

Regular mounted temp sensors on top of the HDPE pipe loose about 5F, mounted on metal it is about 2-3 degrees. You can insulate them a bit, and use heat transfer compounds, you might gain 1 degree accuracy. We have to calibrate all the sensors mounted on our WEL monitoring. The only good way is a calibrated digital needle thermometer and p/t ports.

 

Just answer my question.

Don't confuse me with facts and inconvenient truths

 

This is exactly as I do for EWT and LWT measurements.

The five key things I have found for maximally accurate EWT/LWT temp readings:

1. Place sensors on copper pipe inside the unit.
2. Small amount of heat sink thermal grease on pipe and sensor before placing sensor on pipe.
3. Firm mechanical attachment of sensor to pipe (i.e. zip tie).
4. Wrap sensor wires around pipe for a few loops - helps to isolate ambient temp influencing sensor via wiring.
5. Insulate sensor from ambient air.

Step 5 (insulation) is by far the most important step, by a long shot. Step 3 (mechanical fastening) is the second most important step. The other 3 steps provide incremental improvement. For steady-state readings, step 1 (placement on copper pipe) is not necessary - using the HDPE pipe is fine.

Best regards,

Bill

 

I would add that calibration is crucial! Compare your readings with the actual water temps inside the pipe.

 

The aluminum foil tape routinely used for ductwork provides an excellent mechanical and thermal connection for thermistors to pipes / tubes / whatever else whose temperature is of interest.

Iced water (32*F) and boiling water (212*F) provide cheap field calibration points. Isolation from ambient air is critical to inferring fluid temps from tube wall temps.

 

docjenser - This may seem like a simple question, but how to you figure out the GPM with a given pump. I am pretty sure I have a grundfos 26-99 pump with a little over 4000' of 3/4" pipe in the ground.

 

Pressure drop calculation for the loop and the heatpump (and everything else the water flows through), and then matching it with the pump curve for your specific pump. It is called "riding the curve". What heatpump do you have, how much header pipe inside and outside the house, number of elbows, how many circuits and how big is the header and loop pipe. Then you know your system pressure drop from at a certain flow rate. Then you look at the pump curve and see how many GPM the pump does at a certain pressure.