TRICOIL Performance Calculator

ℹ How to Use This Calculator

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TRICOIL traces the cooling-coil air process on a psychrometric chart and calculates the room sensible load, latent load, and coil performance. It is designed for single-zone systems with any mix of outside and return air — from 0 % to 100 % OA.

STEP 1 — Set Outdoor Design Conditions

Type a city name in the Design Location picker and select a design frequency (0.4 % / 1 % / 2 %). Click Apply to load outdoor dry bulb and wet bulb.

Use Cooling (DB/MWB) for most projects. Switch to Dehumidification (DP/MCDB) when outside air fraction exceeds roughly 30 % or when latent load governs — labs, hospitals, school gyms, 100 % makeup-air units. The dew point and mean coincident dry bulb fill automatically from ASHRAE 2017 Table 1; verify against your project-specific tables before finalizing.

STEP 2 — Enter Airflows and Room Conditions

Enter Outside Air CFM and Return Air CFM (supply = OA + RA). Set the Room DB and RH % — 75 °F / 50 % is a common starting point. The mixed-air state (Point A) updates instantly as you type.

STEP 3 — Set Coil Leaving and Supply Air Conditions

Point C is the air leaving the cooling coil — enter DB and WB to match your coil selection or target ADP. Point D is the supply air delivered to the room — equal to C for a DX system; slightly warmer for systems with reheat or fan heat downstream of the coil. Adjust the Coil Efficiency slider to position D automatically, or drag it on the chart.

Reading the Psychrometric Chart

A — Mixed air entering the coil
B — Apparatus dew point (coil process direction)
C — Air leaving the coil
D — Supply air into the room
Room — Design room condition
The D→Room line is the Room Sensible Heat Factor line. If D lies on the RSHF line through the room point, the coil is correctly sized for both sensible and latent load simultaneously.

Drag to Explore

Each labeled point on the chart has a dashed-circle drag handle. Grab and drag:
C — slides along its constant-RH curve (coil physics); adjusts latent capacity
D — moves horizontally (constant humidity ratio); simulates reheat or fan heat
Room — repositions the design room condition freely

The Live Load Box (lower-right of the chart) updates in real-time — Total Cooling (tons), Sensible (MBH), Latent (MBH), and RSHF. Use this to confirm the coil selection satisfies your load calculation.

Typical Design Workflow

Select location → Apply outdoor conditions
Enter OA CFM, RA CFM, room DB & RH
Set Point C to match coil leaving conditions
Scroll below the chart → press ▶ Calculate Performance
Confirm D→Room RSHF line aligns with room load
Check Live Load Box — Total & Latent satisfy load calcs
If latent governs, switch to Dehumidification design and repeat

All psychrometric calculations use ASHRAE IP equations at standard atmospheric pressure (14.696 psia / sea level). Results are for design verification — always cross-check against coil manufacturer's certified data.

Design Location — ASHRAE 2017 Outdoor Conditions

City / Station

Design %

Design Basis

Cooling Season Inputs

Point A — Mixed Entering Air (Calculated)

Outside Air

Dry Bulb (°F)

Wet Bulb (°F)

Air Volume (CFM)

Room Return Air

Dry Bulb (°F)

Rel. Humidity (%)

Air Volume (CFM)

↓ mixed entering air ↓

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Dry Bulb (°F)

—

Wet Bulb (°F)

—

Rel. Humidity (%)

—

Total CFM

Point C — Primary Coil Leaving

Dry Bulb Temp (°F)

Wet Bulb Temp (°F)

Point D — Reheat Leaving / Supply

Run-Around Coil Efficiency (%)

Calculated Supply DB (°F)

T_D = T_C + ε × (T_A − T_C) | Higher efficiency requires more coil surface area. 45% is the practical maximum.

Point E — Supply Air (After Fan)

Fan Heat Rise (°F)

Calculated Supply DB (°F)

T_E = T_D + fan heat rise | W unchanged through fan.

Heating Season Inputs

Outside Air Dry Bulb (°F)

Supply Air Temp (°F)

Air Volume (CFM)

Psychrometric Chart

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Press the Calculate Performance button to populate this chart

Scroll below this chart and click ▶ Calculate Performance. Point A updates as you type — the full A→B→C→D process path and load results require Calculate.

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Psychrometric States — Cooling Season

Property	A — Mixed Entering	B — After Precool	C — After Primary Coil	D — After Reheat	E — Supply (After Fan)

Performance Comparison

Cooling Season	Value	Unit

Heating Season	Value	Unit

Takeaway Summary

Project Name

Date

Calculate performance first to generate the takeaway.