Commissioning BTU meters

[tbedford]

Good morning all,

On my last project I tried to verify and calculate the Btu energy and compare this to 5 Badger 380HS energy meters installed in a solar and heat pump loop. Nothing is perfect in the field and of course, meter installtion is no exception. There were a number of factors to potentially affect flow and reduce the enrgy transfer.

However all my calculations came up with a BTU energy approx 40 to 50% less than the "factory-calibrated" meters. Something is not quite correct.

I used the formula Q + flow(gpm) x delta T(F) x 500.

Is this formula too simplistic?

Thank you for your help,

Tom

 

[DRWeig]

Hi Tom,

I'm familiar with the Badger 380 --

Need lots more detail, whatever you can provide. What flow rates, what size pipe, what entering and leaving temperatures, etc...

A diagram would be great as well.

Let us know more, and we can perhaps give opinions.

Good on ya,

Goober Dave

 

[btrueblood]

Were you using plain water, or a water/glycol mix? Added glycol will reduce BTU transfer by amounts similar to the 50% you measured.

 

[tbedford]

Thanks and sorry for not responding sooner...
The building is for the local office of an electricity utility provider. Building includes offices and a large truck bay. It is not large say 20,000 sq.ft.
The project is using a geo-source heat pump(30 tons) with gas-fired boilers and a solar system to provide hot water supply for radiant floor heat.
There are three small (less than 3 tons) ceiling mounted water-to-water heat pumps to provide cooling in a separate loop...pump controlled by a VFD.
There are two large ERV's to recapture building heat from exhaust. Each ERV has a hot water coil which is also to act as a cooling coil should OAT and inside conditions require this. Chilled water supply set to 54F.
So pipe sizes are different but none larger than 2". Flow rates vary depending on application..from 90 gpm for the main loop to as low as 15 gpm for the loop serving the three water source heat pumps.
Hot water supply is 160F at the boiler loop (by engineer's design and could be lower as the domestic hot water demand is minimal; set to 110F) to the hydronic loop heat exchanger. Floor radiant loop is variable depending on season and requirements. The floor is also meant to be used for cooling...as needed.

The energy meters (9 total plus the nat gas) are meant to monitor and compare energy transfer between the geo loop, solar loop, heat pump loop, domestic hot water and various heat exchangers. The natural gas meter has an input so total BTU's into the building can be calculated. Power is also being recorded into Building Automation.

I downloaded badger meter software and verified operation of all meters.
One has a red light fault (indicating "other") and I can't find a reference for this on the net.

We don't live in a perfect world with perfect piping and perfect flows and sensors, but I am curious.

I can calculate energy transfer as noted above, but it can and has been radically different than what the meter indicates. So actual energy is likley somewhere between the two...but where??

Thank you,
Tom

 

[DRWeig]

Hi, good info Tom.

I guess my concerns in such small equipment would be the fluid velocity range you're seeing and the temperature differences -- plus, you mention a gas burner, whose efficiency might be unknown.

1) Your BTU meter will do better at higher velocities. The flow sensor's ability to produce accurate results depends on staying within its published range. You told us pipe sizes and flow rate range, but we need to know velocities. It would help if you had a list of loops to which these are connected, with the flow velocity range in each and the differential temperature range in each.

2) If delta-T is small, your accuracy will go to pot. I've seen loops operating at 2°F delta-T (particularly with heat recovery equipment and oversized chilled water plants). You can't get an accurate reading down there when your temperature sensors can be ±0.5°F. What sort of delta-T range are you experiencing?

3) I assume the gas fired boiler is included in your energy balance (it's unclear from what you've told us), are you certain of the burner's efficiency, even at part loads? It's hard to rely on manufacturers data, it's just too easy to get combustion air out of whack.

Let's see if any of the others have comments...

Good on ya,

Goober Dave

 

[danw2]

As mentioned, the delta T is typically low and one can't afford temperature mismeasurements.

I looked at the Badger 380 specs and installation sheet.
They are somewhat silent on temperature measurement, providing no installation recommendations, only a spec of Class B accuracy. You can interpolate the accuracy for your temperature range:

It isn't clear whether the remote temperature sensor (the one that is not built into the flowmeter housing) is clamp-on style or designed for insertion into a thermowell.

If it is clamp-on, you have to be careful that it's not mounted on 8 layers of paint or worse, loosened paint or rust, which will elevate the RTD from the pipe surface and let it see the ambient air temp.

Badger does not mention thermal conductive paste and whether it's clamp-on or thermowell, the clamp-on joint between the RTD and pipe or the air gap in a thermocwell should be generously filled with thermal conductive paste.

I install insulation over the RTD area to avoid thermal drafts which affect the RTD.

Clamp-ons need to be well secured to the pipe.

There is undoubtably some temp calibration procedure. An ice bath is not that hard to come up with to test the remote RTD to see how far it is from 0.00°C.