Revit MEP HVAC load calculation Report Analyses
In this tutorial, Afocus on analyzing the HVAC load calculation report in detail using Revit MEP. In the previous lecture, you learned how to calculate HVAC loads with Revit MEP. Now, we'll review the complete cooling and heating load report. First, we’ll generate the report using Revit MEP, then explore each section step by step. Let’s dive into Revit MEP
Step 1: Cooling Load Report Analyses (Revit MEP)
analyze the above report in two steps
Analyses 1
1. Conditions at Time of Peak
Peak Time: 7/21 at 3:45 PM (when cooling demand is highest).Outside Conditions:
- DB (Dry Bulb Temperature): 94.9°F (air temperature).
- HR (Humidity Ratio): 0.0150 lb/lb (amount of water in the air).
- WB (Wet Bulb Temperature): 76.0°F (temperature including moisture effects).
Inside Zone Conditions:
- DB: 75.0°F (comfortable room temperature).
- HR: 0.0098 lb/lb (less moisture inside than outside).
- RH (Relative Humidity): 53.0% (moderate humidity level indoors).
2. Engineering Checks
- Capacity per Floor Area: 52.96 Btu/hr-ft² (energy needed per square foot to cool the space).
- Floor Area per Capacity: 18.8814 ft²/kBtu-hr (space area served by 1,000 Btu/hr).
- Outdoor Air Percentage: 13.56% (portion of air from outside for ventilation).
- Airflow per Floor Area: 2.0444 ft³/min-ft² (amount of air moving in cubic feet per minute for every square foot).
- Airflow per Capacity: 463.2244 ft³/min-ton (air needed to cool 1 ton of load).
- Number of People: 408.0 (occupants in the zone).
Analyses 2
3. Peak Loads [Btu/hr]
Cooling: 42,010 Btu/hr (blue part of the pie).
Heating: 36,111 Btu/hr (red part of the pie).
4. Cooling Load Components [Btu/hr]
Conduction (dark blue): 457,633 Btu/hr (largest part of the chart).
Solar (orange): 98,452 Btu/hr.
Equipment (yellow): 234,949 Btu/hr
.Outdoor Air (light pink): 13,962 Btu/hr
.People (purple): 12,136 Btu/hr.
Lights (light purple): 2,192 Btu/hr.
Other (tiny section): 1,396 Btu/hr.
Analyses 3
Detailed Analysis of the Table
This table provides an in-depth breakdown of the cooling load for a zone. Here's the analysis step-by-step:
1. Categories Explained
The table divides the cooling load into three main categories:
- Envelope: Heat entering the building through walls, roof, windows, etc.
- Internal Gains: Heat generated inside the building by people, lights, and equipment.
- Systems: Heat from ventilation systems and other mechanical operations.
Each category is further broken down into:
- Instant Sensible: Heat that affects the temperature immediately.
- Delayed Sensible: Heat absorbed by the building materials and released later.
- Latent: Heat related to moisture (e.g., humidity).
2. Key Insights by Section
Envelope
- Roof: Contributes 246,375 Btu/hr (58.5% of the total load). It’s the largest contributor, indicating poor insulation or high heat absorption.
- Glass - Conduction: Adds 1,204 Btu/hr, a small but measurable impact.
- Glass - Solar: Adds only 162 Btu/hr (minimal impact).
- Slab (Floor): Has a negative value (-156,620 Btu/hr), which means the slab is cooling the space by absorbing heat rather than adding to it.
- Partition: Reduces heat by -38,607 Btu/hr, contributing to cooling.
- Total Envelope Contribution: 54,774 Btu/hr (13% of total).
Internal Gains
- People: Major source of heat: 234,949 Btu/hr (55.8% of total). People contribute both sensible heat (body temperature) and latent heat (moisture from breathing).
- Lights: Add 21,922 Btu/hr (5.2%), which is purely sensible heat.
- Equipment: Contributes 12,309 Btu/hr (2.9%) due to heat released by devices.
- Total Internal Gains Contribution: 269,180 Btu/hr (63.9%).
Systems
- Zone Ventilation: Adds 98,452 Btu/hr (23.4%), primarily latent heat from outdoor air.
- Other system components like transfer air, DOAS (Dedicated Outdoor Air Systems), and HVAC equipment losses contribute negligible amounts.
- Total Systems Contribution: 98,452 Btu/hr (23.4%).
3. Totals
- Grand Total Cooling Load: 421,010 Btu/hr (100%).
- Sensible (Instant + Delayed): 317,428 Btu/hr (75.4%).
- Latent (Humidity): 103,581 Btu/hr (24.6%).
4. Observations and Recommendations
- Roof Dominance: The roof is the largest source of heat gain, contributing nearly 58.5% of the envelope load. Improved roof insulation or reflective roofing materials can reduce this significantly.
- People’s Contribution: Human activity is responsible for 55.8% of the total cooling load. This is normal in spaces with high occupancy (e.g., offices or auditoriums).
- Latent Load: A significant portion (24.6%) is latent heat, suggesting high humidity control requirements. Dehumidifiers or better ventilation strategies may help.
- Slab Cooling Effect: The negative load from the slab indicates it absorbs heat. This is a cooling benefit and should be maintained.
- Lighting Efficiency: Lights contribute 5.2%. Using energy-efficient lighting (e.g., LEDs) can further reduce this load.
Step 2 : Heating Load Report Analyses
Analyses 1
1. Conditions at Time of Peak
- Peak Time: January 21 at midnight (24:00), indicating this is a winter scenario.
- Outside Conditions:
- DB (Dry Bulb): 8.4°F (extremely cold air temperature).
- HR (Humidity Ratio): 0.0012 lb/lb (very low moisture in the air).
- WB (Wet Bulb): 8.4°F (dry and wet bulb temperatures are similar due to low humidity).
- Inside Zone Conditions:
- DB: 70.0°F (target comfortable temperature).
- HR: 0.0048 lb/lb (higher humidity than outside but still low).
- RH (Relative Humidity): 30.9% (dry indoor conditions).
2. Engineering Checks
- Capacity per Floor Area: -45.43 Btu/hr-ft² (negative values suggest cooling effects; could be an error or unique calculation factor for heating).
- Floor Area per Capacity: Not available (likely a data input issue).
- Outdoor Air Percentage: 13.56% of ventilation is from outside air.
- Airflow per Floor Area: 1.2888 ft³/min-ft² (airflow for heating the space efficiently).
- Airflow per Capacity: Not calculated (likely irrelevant for this specific heating setup).
- Number of People: 408 occupants, adding heat from body warmth.
3. Peak Loads (Btu/hr)
- Heating Load: 36,111 Btu/hr.
- Cooling Load for Comparison: 42,010 Btu/hr (as reference from cooling).
4. Heating Load Components
- Conduction: Dominates at 421,603 Btu/hr. This is the heat loss through walls, roof, windows, etc., which the system must compensate for.
- Solar: Very small contribution of 136 Btu/hr (minimal solar heat gain during peak winter).
- Equipment, Lights, and People: No notable contributions to heating, as these are more relevant to cooling scenarios.
- Outdoor Air: 29,021 Btu/hr (represents the heat loss due to bringing in cold outdoor air for ventilation).
5. Observations and Recommendations
- Conduction as the Major Contributor: At 421,603 Btu/hr, most of the heating requirement is due to heat loss through building elements (walls, roof, windows, etc.). Improving insulation can significantly reduce heating needs.
- Outdoor Air Load: Ventilation adds a 29,021 Btu/hr heating load. Heat recovery systems could pre-warm incoming air to reduce this burden.
- Minimal Internal Gains: Unlike cooling, heating doesn't benefit much from lights, equipment, or occupants in this scenario. The focus is purely on compensating for environmental losses.
- Heating System Efficiency: Data gaps like "Airflow per Capacity" and "Floor Area per Capacity" may need to be resolved for a clearer understanding of heating system performance.
Analyses 2
1. Envelope
This category refers to heat transfer through the building's structure, such as the roof, walls, and floor.
- Roof:
- Instant Sensible: 0 Btu/hr
- Delayed Sensible: 246,375 Btu/hr
- Latent: 0 Btu/hr
- Total: 246,375 Btu/hr
- Percent of Total: 58.5%
- Other - Roof, Ceiling, Glass - Solar, Door, and Other Wall:
- These have no significant contributions (all values are 0 or very small).
- Glass - Conduction:
- Instant Sensible: 1,204 Btu/hr
- Total: 1,204 Btu/hr
- Percent of Total: 0%
- Wall:
- Delayed Sensible: -6,283 Btu/hr
- Total: -6,283 Btu/hr
- Percent of Total: -1.5%
- Partition:
- Delayed Sensible: -38,607 Btu/hr
- Total: -38,607 Btu/hr
- Percent of Total: -9.2%
- Slab (Floor):
- Delayed Sensible: -156,620 Btu/hr
- Total: -156,620 Btu/hr
- Percent of Total: -37.2%
- Infiltration (Air Leakage):
- Instant Sensible: 3,983 Btu/hr
- Delayed Sensible: 0
- Latent: 4,525 Btu/hr
- Total: 8,508 Btu/hr
- Percent of Total: 2.0%
- Subtotal for Envelope:
- Instant Sensible: 5,187 Btu/hr
- Delayed Sensible: 45,062 Btu/hr
- Latent: 4,525 Btu/hr
- Total: 54,774 Btu/hr
- Percent of Total: 13.0%
2. Internal Gains
This category represents heat generated within the building due to occupants, lights, and equipment.
- People:
- Instant Sensible: 65,170 Btu/hr
- Delayed Sensible: 123,079 Btu/hr
- Latent: 46,700 Btu/hr
- Total: 234,949 Btu/hr
- Percent of Total: 55.8%
- Lights:
- Instant Sensible: 21,922 Btu/hr
- Total: 21,922 Btu/hr
- Percent of Total: 5.2%
- Equipment:
- Instant Sensible: 12,309 Btu/hr
- Total: 12,309 Btu/hr
- Percent of Total: 2.9%
- Subtotal for Internal Gains:
- Instant Sensible: 99,401 Btu/hr
- Delayed Sensible: 123,079 Btu/hr
- Latent: 46,700 Btu/hr
- Total: 269,180 Btu/hr
- Percent of Total: 63.9%
3. Systems
This category includes heat contributions or losses from ventilation and other mechanical systems.
- Zone Ventilation:
- Instant Sensible: 46,095 Btu/hr
- Latent: 52,357 Btu/hr
- Total: 98,452 Btu/hr
- Percent of Total: 23.4%
- Other System Components:
- These contribute 0 to the load in this table.
- Subtotal for Systems:
- Instant Sensible: 46,095 Btu/hr
- Latent: 52,357 Btu/hr
- Total: 98,452 Btu/hr
- Percent of Total: 23.4%
4. Totals
This row summarizes the total contributions across all categories.
- Instant Sensible: 150,683 Btu/hr (35.8% of total load).
- Delayed Sensible: 166,745 Btu/hr (39.6% of total load).
- Latent: 103,581 Btu/hr (24.6% of total load).
- Grand Total Load: 421,010 Btu/hr (100%).
5. Additional Adjustments
- Sizing Factor Adjustment: 0 Btu/hr (no adjustment made).
- Time Delay Correction: -1,396 Btu/hr, adjusting for delayed heat not reflected in instant values.