Lecture 8

DETD/ DCLF Method

- DETD: design equivalent temperature difference - DCLF: design cooling load factor - correlates transient problem back to steady state equation through charts and tables

determine people heat gain

- determine activity - use sensible heat gain/ persons in table F.8 (11th) or G.8 (12th) - determine number of people or use occupancy density in table E.25 (11th) or F.1 (12th) - either number of seats or table

purpose of load calculations

- determine thermal requirements to maintain thermostatic settings - what the HVAC system has to provide for comfort - sizing of: fan and ductwork and primary equipment - not how much energy create throughout the entire life of building

Equipment

- electric driven devices: computers, printers, etc. - electricity eventually converted to sensible heat - sensible gain per unit area in Table F.3A/ G.3A - errors ... see notes and correct in book - determining equipment load: use sensible gain x area - do not use nameplate ratings to determine thermal load

Energy Calculations

- long- term (seasonal or yearly) summation of energy consumption of building - must look at actual or average weather trend not single data point - evaluate energy efficiency of building and HVAC design (not done by load calculations)

sensible cooling loads

- not a feasible hand calculation: accuracy a concern in hand calc, so instead use credible computer simulations when possible - BUT hand calculations do allow approximation of individual envelope components

what load calculations are not

- perfect: usually some oversizing takes place for "safety" (oversizing causes more money because the larger the system is the more complex and more money engineers require) - energy calculation: loads are a snapshot in time, cannot be extrapolated, and won't tell how efficient building design is (only use for that purpose and not others)

Internal Heat Gains

- something that generates heat within a space - add to potential cooling needs - not limited to peoples lights, and equipment - even a cell phone adds some heat and must take into account

Lights

- visible gain for lights - sensible gain per unit area in table F.3B (11th) or G.3B (12th) - Table: DF= daylighting factor, sensible heat gain from daylighting (electric) - architectural design determines about of artificial light needed - lights add heat to a space - summer/ cooling: effective daylighting decreases cooling needs - winter/ heating: artificial lights decrease heating needs... but is that a good thing? - determining light load: multiply gain/ area from table F.3B (11th) or G.3B (12th)/ Alternatively: count "wattage" of fixtures in space

DETD/ DCLF Step 5

Calculate cooling loads - sum all heat gains from step 1-4 cooling load must balance all heat gains - see notes for equation - heating and cooling loads: use larger so can have big enough ducts

DETD/ DCLF Step 4

Internal Gains - People in table F.8 (11th) or G.8 (12th) - lights in table F.3B or G.3B - equipment in table F.3A (11th) or G3.A (12th)

DETD/ DCLF Step 2

Window gains - find the DCLF in table F.6 (11th) or G.6 (12th) - sum for all windows

Are energy simulation programs useful?

Yes: don't have to calculate by hand - not only load but energy numbers as well - is prof. Strand biased? yes because has rights to EnergyPlus - Does it matter that Prof. Strand is biased? no many people using these programs (field says so with sustainability) - Are hand calculations worthless? No shows where heating/ cooling loads are coming from. gives an idea of numbers in studio and says where largest loads are coming from

People

add heat to space - sensible: convection and radiation - Latent: evaporation (breathing and sweating) - varies by activity - F.8 (11th Edition) or G.8 (12th edition) - look at sensible heat column - latent adds moisture but will not look at that right now - take number and multiply by number of people to tell you heat gain

use of software

building energy modeling software used for/ by: - all stages of design - providing more accuracy than hand calculations - enabling evaluation of various alternatives and technology - many leading firms in design process - rating systems and standards

computer software

building energy/ load simulation programs: - EnergyPlus (developed at UIUC) -Energy-10 (no longer being updated) - eQuest - ESP-r (UK developed and popular) - TRNSYS (UW Madison developed) - and others...

DETD/ DCLF Step 1

heat transfer gains - opaque surfaces only - find DETD from Table F.5 (11th) or G.5 (12th) - sum contribution of all surfaces - use chart to find numbers - determined by outside design temperature

DETD/ DCLF Step 3

infiltration gains - similar to heating load (different ACH) - treat ventilation as part of HVAC load

Sensible load calculation summary

reminder: handout available, to be distributed via email...

Sensible load Comparison

see in notes