The FMCS is indicating that the Y-mid is 72F at this time. Knowing that a new HVAC control system has recently come on line, as well as the knowledge that the Y-mid VEA temp had been "high" at one point last week (at the time, I had noticed increases in pump currents for all Y-mid AIPs which is typical of an increase in room temperature. I confirmed with Bubba at that time that he was aware of the increase room temp.) I decided to independently measure CP3. See attached image. This is only "interesting" and no conclusion should be made as nothing is calibrated yada yada yada.........
I wonder what's cheaper: LN2 at 35 cents a gallon or electricity at 6 cents a kWh.
According to PSI V049-1-033 (aka LIGO-C960964, attachment 4, p. 98 ff) the short CP in “iced” surface condition (thermal emissivity ~ 0.9) absorbs 250W thermal blackbody radiation from each end aperture, assuming 80K reservoir and 300K beamtube or chamber blackbody temperature. Another 102W are expected to enter through conduction, supply line loss, and local shell radiation [1].
With other factors fixed (i.e., midstation climate-controlled, pipe insulation good, etc.) the boiloff rate vs. variable beamtube temperature can be approximated as
mdot ~ P/C
~ [352W + 250W*(T_bt/300K)^4 ] / C
~ (602W + 1000W*[(T_bt-300K)/300K])/C
= 2.6 g/s @ T_bt = 0C, 3.0 g/s @ 27C, and 3.2 g/s @ 40C (32, 81 and 104 F respectively)
where mdot is mass evaporation rate (g/s), T_bt is the beamtube temperature, P is absorbed thermal power (W), and C is LN2 heat of vaporization (~ 200 J/g).
In other words, short CP LN2 consumption should increase by about 0.6 % per degree C of beamtube temperature [2].
We should install BTE thermometers as done at LLO. Just one or two per module would probably be adequate.
[1] The PSI calc assumes heat shielding and reflective liners built into the CP have very low emissivity (< .05), which may not be true any more; if the tube liner finish or cleanliness is compromised due to age, radiant heat load could be 1.5x greater.
[2] At LLO naked tube steel now tracks BTE enclosure air temperature closely [G1400433]. BTE air temp is a function of outside ambient, sun exposure and the insulating and heat storage properties of the BTE concrete, but we think both sites hit at least 49C peak in summer. Diurnal variation is about 20C p-p.