Field measurement and modeling of UVC cooling coil irradiation for heating, ventilating, and air conditioning energy use reduction (RP-1738)—Part 1: Field measurements

Figures & data

Table 1. Site and HVAC system characteristics.

	Tampa (climate zone 2 A)	PSU (climate zone 5 A)
System type	Variable air volume (VAV)	Constant Air Volume (CAV)
Design supply airflow	6000 cfm (2.832 m^3/s)^i	17,000 cfm (8.02 m^3/s)
Design airside pressure drop	1.0 in. wg. (249.1 Pa)^ii	0.94 in. wg (234 Pa)
Design outdoor airflow	500–1500 cfm (0.24–0.71 m^3/s)^iii	5000 cfm (2.36 m^3/s)
OA intake location	Wall, 10–15 ft (3.1–4.56 m) above grade	Rooftop
Filter type and location	Unlabeled flat plastic mesh media, directly upstream of cooling coil	MERV 8 in “W” formation, upstream of cooling coil and air blender
Design water flow	50 gpm (3.16e-3 m^3/s)^iv	PSU: 89.3 gpm (5.63e-3 m^3/s)
Design water entering and leaving	42°F (5.56 °C)	44°F (6.67 °C)
temperature	58.3°F (14.6 °C)	54°F (12.2 °C)
Total coil capacity	225 MBH (65.9 kW)^v	727 MBH (213.1 kW)
Sensible coil capacity	153 MBH (44.8 kW)^v	504 MBH (147.7 kW)
Coil dimensions (W × H)	60 by 33 in (1.52 by 0.84 m)	Lower: 81 by 30 in (2.06 by 0.76 m)
		Upper: 81 by 27 in (2.06 by 0.69 m)
Coil depth	6 rows	6 rows, each coil
Coil fins	8/inch (3.15/cm)	11/inch (4.33/cm), both coils
Coil maintenance	Irregular	Irregular
Function of area served	Science classroom space	Strength training and cardiovascular fitness with some corridor space
Occupancy and schedule	College students and instructors, hours of use dependent on class schedules	Gym users (college students and staff), early morning to late evening, except holidays

ⁱ Design value was not available, estimated using 450 fpm (2.29 m/s) face velocity and checked against measured flow.

ⁱⁱ Design value was not available, estimated based on measured data.

ⁱⁱⁱ Variable with fume hood operation.

^iv Design value was not available, estimated using Tampa outdoor design conditions, measured SA/OA flow, and assumed waterside ΔT = 10°F (5.56 °C). Checked against measured flow.

^v Design value was not available, so estimated using Tampa outdoor design conditions and measured SA/OA flow.

Fig. 1. Image of fouling at Tampa site, downstream side of coil. Visible fouling is fungal growth.

Fig. 2. Close-up of fouling at PSU site, upstream side of coil. Note the accumulation of fouling at the space between the tubes.

Table 2. Field site UV lamp information.

Site	Rows	Lamps per row	Lamp output	UV placement
Tampa	2	1 × 21in (53.3 cm)	23 W	Downstream of coil
		1 × 61 in (154.9 cm)	72 W
PSU	2 (1 per coil)	1 × 24 in (61.0 cm)	17 W	Upstream of coil
		1 × 36 in (91.4 cm)	30 W

Table 3. Measurement instrumentation.

Point	Accuracy	Manufacturer and model	Notes
SA flow (Tampa)	±2% of reading	Ebtron GTx116-P Duct Probes	Thermal dispersion sensors
SA flow (PSU)	±2% of reading	Ebtron GTx116-F Fan Inlet Sensors	Thermal dispersion sensors
Air ΔP	±0.14% full scale±0.0035 in. wg(±0.872 Pa)	Setra 239Full scale: 0–2.5 in. wg (0–623 Pa)	NIST-traceable calibrated. Per manufacturer literature, accuracy is combination of nonlinearity, hysteresis, and nonrepeatability.
EAT and LAT	±0.36°F (±0.2 °C)	Burns 15927 Averaging RTD	RTD = resistance temperature detector
			Averaging RTD in Z-formation across coil face
Entering and leaving RH	±1% RH	Vaisala HMT330	NIST-traceable calibrated
CHW flow	±2% of reading	Dynasonics TFX Ultra	Clamp-on ultrasonic flow meter
EWT and LWT	±0.36°F (±0.2 °C)	Burns 200 Series RTD	RTD = resistance temperature detector
			In thermowell installed in chilled water piping

SA = supply air, EAT = entering air temperature, for example, upstream of the coil. LAT = leaving air temperature, for example, downstream of the coil. RH = relative humidity. CHW = chilled water. EWT = entering water temperature, into the coil. LWT = leaving water temperature, out of the coil.

Fig. 3. Instrumentation schematic (T = temperature, RH = relative humidity, DP = pressure differential, CHW = chilled water piping).

Fig. 4. Use of coil model in typical and inverse applications.

Table 4. UA model use of input variables in simulation software.

Input	Coil	Coil	UAop
variable	design	operation	calculation
Airflow rate	X	X	(Design and operation)
Water flow rate	X	X	(Design and operation)
Inlet air temperature	X	X	(Design and operation)
Inlet air humidity ratio	X	X	—
Inlet water temperature	X	X	(Design and operation)
Outlet air temperature	X	—	—
Outlet air humidity ratio	X	—	—

Table 5. Conditions for design UA value calculation.

Parameter	Value
Inlet air dry bulb temperature	80.00°F (26.67 °C)
Inlet air wet-bulb temperature	67.00°F (19.44 °C)
Inlet chilled water temperature	44.00°F (6.67 °C)
Design airflow rate	See Table 1
Design water flow rate	See Table 1

Fig. 5. Tampa site coil before application of UVGI.

Fig. 6. Tampa site coil after 13 months of UVGI exposure.

Table 6. Binning range and interval for analysis of Tampa ΔP data.

	Min	Max	Interval
Airflow	3800 cfm 1.79 m^3/s	5000 cfm 2.36 m^3/s	200 cfm (6 bins) 0.094 m^3/s
Latent Load	34.1 kBTU/h 10 kW	102 kBTU/h 30 kW	3.4 kBTU/h (20 bins) 1 kW

Fig. 7. Tampa mean airside pressure drop versus time for example bins; a. 3800–4000 cfm and 44.4–47.8 kBTU/h (1.79–1.89 m³/s and 13–14 kW latent load); b. 4000–4200 cfm and 51.2–54.6 kBTU/h (1.89–1.98 m³/s and 15–16 kW). Error bars are ±2% of full scale for illustration, as the calculated standard deviations using the point measurement error of 0.14% full scale were too small to be visible.

Fig. 8. Tampa mean pressure drop improvement across all months and all bins.

Table 7. Binning range and interval for analysis of PSU ΔP data.

	Min	Max	Interval
Airflow	14,000 cfm 6.61 m^3/s	15,000 cfm 7.08 m^3/s	200 cfm (5 bins) 0.094 m^3/s
Latent load	34.1 kBTU/h 10 kW	154 kBTU/h 45 kW	8.5 kBTU/h (14 bins) 2.5 kW

Fig. 9. PSU mean air side pressure drop versus time for example bins; a. 14,200–14,400 cfm and 57.9–68.2 kBTU/h (6.61–6.70 m³/s and 17.5–20.0 kW); b. 14,200–14,400 cfm and 68.2–76.8 kBTU/h (6.61–6.70 m³/s and 20.0–22.5 kW). Error bars are ±2% of full scale for illustration, as the calculated standard deviations using the point measurement error of 0.14% full scale were too small to be visible.

Fig. 10. PSU mean pressure drop improvement across all months and all bins.

Fig. 11. Tampa UA versus time. Red line denotes when UV is turned on.

Fig. 12. Tampa UA vs. time, 0.60–0.65 SHR. Error bars are included, but are not visible.

Fig. 13. Tampa percentage improvement in UA versus SHR. Horizontal axis values represent the upper limit of a 0.05-width bin.

Fig. 14. PSU UA versus time. Red line denotes when UV is turned on.

Fig. 15. PSU UA versus time, 0.80–0.85 SHR.

Fig. 16. PSU percentage improvement in UA versus SHR. Horizontal axis values represent the upper limit of a 0.05-width bin.