HVAC Rule of Thumb Calculator Table of Contents 1.0 Introduction ...... 2 1.1 Units ...... 2 2.0 Disclaimer ...... 3 3.0 How to use this Calculator ...... 4 4.0 Selecting Inputs ...... 5 4.1 Building Information ...... 5 4.1.1 Building Area ...... 5 4.1.2 Building Types ...... 6 4.1.3 Building Shape ...... 10 4.1.4 Building Information for Heating ...... 10 4.1.5 Building Location ...... 11 4.2 Choosing the Cooling System Type ...... 12 4.2.1 Split System ...... 12 4.2.2 Air Cooled Chilled Water System ...... 13 4.2.3 Water Cooled Chilled Water System ...... 15 4.3 Choosing the Heating System Type ...... 16 5.0 Understanding the Outputs ...... 16 5.1 Cooling Load ...... 16 5.2 Heating Load ...... 17 5.3 Split System/Packaged Unit Type ...... 19 5.4 Air Cooled Chilled Water System Type ...... 20 5.5 Water Cooled Chilled Water System Type ...... 24
HVAC Rule of Thumb Calc-1 http://www.engproguides.com 1.0 INTRODUCTION During the early stages of HVAC design, it is important to be able to quickly determine the overall size of an HVAC system in order to assist the owner and/or architect space plan and determine rough costs. At these early stages, the space changes very quickly and the owner and/or architect need immediate feedback to be able to ensure that there is adequate space for mechanical equipment and there is sufficient funds.
It takes years of experience to be able to quickly select an HVAC system type, size the HVAC system and cost the HVAC system, with limited information. After designing a multitude of HVAC systems for all sorts of buildings, you should be able to
The calculator uses the building square footage, building usage type and building shape to automatically determine the maximum and minimum overall tonnage and electrical usage of the equipment for multiple HVAC systems. The HVAC systems analyzed in this calculator include (1) split systems/packaged A/C, (2) air cooled chilled water systems and (3) water cooled chilled water systems. This will help you to select equipment, space plan for any mechanical rooms and ceiling space and create a budget. Also by providing electrical values for the equipment, the electrical engineer can also plan for utility service, transformers and panels.
Figure 1: The three systems available in this calculator are the (1) split system, packaged A/C, (2) air cooled chilled water and (3) water cooled chilled water.
1.1 UNITS There are two calculators, (1) one that focuses on United States Customary System Units (USCS) and another on (2) International System of Units (SI). However, this guide focuses exclusively on the USCS.
HVAC Rule of Thumb Calc-2 http://www.engproguides.com Table 1: This table shows a list of the popular unit conversions applicable for this calculator.
1 Btu/h = 8.33 x10-5 tons 1 ton = 12,000 Btu/h 1 Btu/h = 2.93 x10-4 kW 1 kW = 3,412 Btu/h 1 Btu/h = 0.293 W 1 W = 3.412 Btu/h 1 EER = 0.083 kW/ton 1 kW/ton = 12 EER 1 SEER = 0.083 kW/ton 1 kW/ton = 12 SEER 1 feet = 03048 meter 1 meter = 3.2808 feet 1 lb = 0.4536 kg 1 kg = 2.205 lb
1 ft2 = 0.093 m2 1 m2 = 10.7639 ft2 1 gal = 4.41 liters 1 liters = 0.227 gal 1 ft3 = 0.133 gal 1 gal = 7.481 ft3 1 fpm = 5.08x10-3 m/s 1 m/s = 195.85 fpm 1 gpm = 0.063 l/s 1 l/s = 15.85 gpm 1 cfm = 0.472 l/s 1 l/s = 2.119 cfm 1 in. wg = 249.09 Pa 1 Pa = 4.01 x10-3 in. wg 1 ft. hd = 2.99 Pa 1 Pa = 3.34 x10-4 ft. hd 1 psi = 6.89 x10-3 MPa 1 MPa = 145.04 psi 1 psi = 27.68 in. wg 1 in. wg = 0.036 psi 1 psi = 2.31 ft. hd 1 ft. hd = 0.043 psi 1 lb/ft3 = 16.018 kg/m3 1 kg/m3 = 0.062 lb/ft3 1 Btu = 0.293 watthour 1 watthour = 3.412 Btu 1 Btu/h = 3.93x10-4 HP 1 HP = 2,545 Btu/h 1 HP = 0.746 kW 1 kW = 1.34 HP
There are two main sets of units that should be discussed in more detail, (1) EER and (2) SEER. First, you need to understand that the efficiency of air conditioners in the refrigeration cycle is greatly dependent on the heat rejection provided at the evaporator and condenser. In the first figure, you can see that the heat rejection at the evaporator and condenser change from air to water as you move from split system to water cooled chilled water system. This change in heat rejection from air to water greatly improves the efficiency because the heat transfer is much better with water due to its increased heat capacity.
EER: The Energy Efficiency Ratio or EER is the ratio of the total cooling Btu/h to the total input power in watts. The conversion from EER to kW/ton is shown below.