The Fieldpiece SDP2 Dual in Duct Psychrometer

Introduction to the Fieldpiece SDP-2 Dual Indox Cyclometer

Overview of the Tool

• Jim Bergman introduces the Fieldpiece SDP-2 as an essential tool for technicians, highlighting its capabilities in measuring wet bulb and dry bulb temperatures, as well as enthalpy.

• The SDP-2 includes a supply air probe, return air probe, blow molded case, and cones for duct measurements.

Features and Setup

• The instrument measures temperature and humidity simultaneously to calculate various metrics including wet bulb temperature and relative humidity. It can send readings to HD3 or S-MAN 4 devices for superheat calculations.

• Probes are color-coded: red for return air and chrome for supply air. Proper setup involves plugging in probes according to their designated positions.

Using the SDP-2 in Duct Measurements

Installation Process

• Setting up the SDP-2 is straightforward; users must align arrows on probes with corresponding markings on the instrument before powering it on.

• Probes are secured using stops that lock them into place within ducts, ensuring accurate sampling of return air.

Measurement Techniques

• When placing probes, it's crucial to position them away from evaporator coils to allow proper mixing of air for accurate readings.

• The instrument allows users to select measurement units (e.g., per pound), providing options like dry bulb and dew point temperatures.

Calculating Capacity with Differential Enthalpy

Monitoring Changes

• The SDP-2 is set up to measure differential enthalpy; small changes indicate normal drift or residual cooling effects in ductwork.

• Once cooling is activated, rapid changes in enthalpy across the coil are observed as equipment stabilizes.

Final Calculations

• After running for about 10 minutes, enthalpy stabilizes at approximately 7.18 BTUs per pound across the evaporator coil.

• Using airflow data (1,078 CFM), Jim prepares to perform a quick calculation of actual BTU capacity based on measured enthalpy values.

BTU Output Calculation and System Performance

BTU Output and Capacity Measurement

• The formula for BTU output is presented: 4.5 times CFM (1078) times change in enthalpy (7.17), resulting in a calculated capacity of 34,781 BTUs.

• The measured fuel capacity of the appliance is approximately 96% of its nominal capacity (36,000 BTUs), which is typical under current outdoor conditions (70 degrees).

Factors Affecting System Capacity

• The return air temperature is noted to be around 71 degrees, which can further reduce system capacity.

• Relative humidity levels are at about 58%, indicating decent performance but still affecting overall efficiency.

Observations During System Shutdown

• A demonstration involves shutting off the system to observe changes in enthalpy as cooling ceases.

• As the ECM fan ramps down, there’s a rapid decrease in change in enthalpy, illustrating how quickly heat loss occurs when cooling stops.

Changes Post-System Shutdown

• After shutdown, the change in enthalpy drops significantly to about 1.4–1.5, while differential dry bulb temperature remains at a notable change of 10 degrees.

• A shift from mechanical cooling to evaporative cooling occurs; despite low enthalpy changes, dry bulb temperatures indicate continued cooling effects.

Humidity Management Insights

• The transition results in an increase in relative humidity from 58% to 100%, highlighting potential issues with humidity control during evaporative cooling.

• Recommendations suggest that if controlling humidity is critical, it may be beneficial to turn off the fan; however, continuous operation can aid systems where sensible cooling is prioritized.

Practical Implications for Different Environments

• In humid regions like Ohio, slight increases in humidity post-cooling are manageable due to effective two-stage systems that maintain comfort levels.

• Observations reveal that even with high relative humidity readings post-shutdown, significant dry bulb temperature changes indicate ongoing cooling benefits as long as the fan operates.

Advanced Features of Measurement Tools

• Introduction of advanced features such as target evaporator exit temperature calculation and target differential temperature calculations enhances understanding and management of HVAC systems.

Understanding Target Evaporator Temperature and System Performance

Target Evaporator Temperature Insights

• The Target Evaporator Temperature (TET) is set at 52.5 degrees, indicating precise calibration within a 0 to 10th degree range.

• A subsequent reading shows the Target Temperature Drop at 17.2 degrees, with only a 3-degree variance from expected calculations, suggesting accurate system performance.

• The ability to monitor evaporator performance helps identify issues like air bypassing the coil, allowing for quick assessments of potential problems.

Importance of Measuring Capacity

• Measuring capacity is crucial for demonstrating system efficiency to customers; variations in outdoor air and load can significantly affect this metric.

• Airflow issues directly decrease system capacity; both overcharging and undercharging also impact performance metrics significantly.

Tools for Optimal System Operation

• Utilizing instruments like the Field Piece SPD2, STA2, and S-MAN4 ensures systems operate close to factory specifications by focusing on correct airflow and charge.

• Understanding enthalpy measurements enhances knowledge about ductwork dynamics and psychometrics, improving overall air conditioning effectiveness.