Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1. Building Heat Loss

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1 DESIGN HEAT LOSS (part 1) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Building Heat Loss Generally speaking, heat loss occurs in winter or More specifically during any underheated time period* Heat loss is a net flow of heat from the inside environment (warmer) to the outside environment (cooler) Such a heat loss will cause the indoor air temperature to drop (unless the lost heat is replaced) entropy in action A heating system must be provided in order to maintain indoor conditions above those found outdoors (temperature for sure, and perhaps also humidity). The heating system will consume energy (costing money and most likely depleting resources and polluting the environment). The heating system may be passive, active, or hybrid. *see cross-reference to Design with Climate (next slide) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Underheated Period temperature COMFORT ZONE Olgyay visualized climate by plotting many, many points that represent hourly combinations of air temperature and relative humidity for someone (in New York City) exposed to outdoor conditions, this is generally the underheated period (too cold for comfort) Olgyay: Design with Climate relative humidity Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Underheated Period balance point temp Olgyay: Design with Climate for someone directly exposed to outdoor conditions, this is generally the underheated period (too cold for comfort) for someone inside a building this may be the underheated period (outdoor conditions too cold for comfort but with those effects tempered by the building envelope) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Balance Point Temperature This is defined as the outdoor air temperature at which a building without a climate control system needs no heating for occupant thermal comfort The specific balance point temperature is a function of building envelope design and internal heat loads Historically (in the 1940s) balance point temperature was presumed to be around 65 F for a typical singlefamily residence Today, well-insulated houses may have a balance point temperature of 50, 40, or 30 deg F Non-residential buildings tend to have lower balance point temperatures (and more complexity) remember this when using bioclimatic charts (Olgyay or Climate Consultant) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Passive Survivability Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Building Thermal Classifications Envelope-load dominated building The majority of thermal loads are the result of climate (interacting through the envelope) Thus, early design efforts related to energy should focus on the envelope Internal-load dominated building The majority of thermal loads are the result of internal gains (equipment, lighting, people) Thus, early design efforts related to energy should focus on reducing internal gains Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Building Thermal Classifications Envelope-load dominated Internal-load dominated Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Design Heat Loss DESIGN heat loss is a specific heat loss calculated using generally-agreed-upon conditions (standardized analysis conventions) It is one of many heat losses (ranging from zero to some maximum value) that a building will experience over time (as weather conditions change) The design heat loss is the magnitude of heat loss that is typically used to size a building heating system (yes, this means that for many hours of the year the heating system is too big, and for other hours it is too small) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Analysis Conventions At the time of design heat loss: There is no solar radiation There are no occupants in the building There is no equipment operating in the building Electric lighting in the building is off Steady-state conditions prevail (there are no rapid changes in temperature/humidity) Design climate data are used to define the exterior conditions these are logical and reasonable assumptions for a sort-of-worst-case (nighttime) heat loss situation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Implications of the Conventions No solar radiation All above-ground assemblies can be treated alike using the equation q = (U)(A)(Δt) all envelope assemblies see the same exterior conditions; orientation and/or tilt of roof, walls, windows are not of concern No occupants, equipment, lighting There are no internal loads to deal with only envelope heat flows Steady-state conditions prevail Thermal mass (heat storage) is not an important characteristic; it is generally ignored Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Design Climate (Specifically Temperature) Each year has a lowest temperature (as a result of that year s specific weather) weather is what happens now versus climate which occurs over a long period Each annual lowest temperature is generally different (perhaps -12 deg in 2014, 2 deg in 2015, ) So which low temperature should be used for the design of heating systems? Weather data for reasonably long periods have been assembled using statistical analysis and made available to designers as climate data* Design temperature values can be selected from such published data *Climate Consultant uses and displays such climate data sets Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Design Climate Data DB = dry bulb air temperature ASHRAE Handbook 2013 Fundamentals two winter temperatures are suggested to a designer Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 ASHRAE Design Climate Data 99% statistically, an average winter will see temperatures lower than this value for 1% of the hours of the year (1% is 88 hrs) 99.6% the same idea, but only 0.4% of the hours of the year will see lower temperatures (0.4% is 35 hrs) Codes may specify which value must be used for design; if not, the choice is up to the designer based upon project OPR (how critical is comfort, when is the building normally used, how critical is energy efficiency?) In addition, the extreme data set (next slide) provides the statisticallyaverage lowest annual temperature seen for a locale in some design situations this may be a value to consider Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Design Climate Data one more winter temperature is available to a designer ASHRAE Handbook CD Fundamentals provides extensive weather data not available in the hard copy Handbook Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 So Looking at Augusta, GA Design Climate Data 99% the value is 26.1 deg F 99.6% the value is 22.5 deg F Extreme winter the value is 16.2 deg F Which value should be used for design of a climate control system (to provide thermal comfort)? This is an important decision. The chosen value will anchor one end of the Δt variable. Assuming 70 deg indoors, Δt might be ( = 43.9) or ( = 47.5) or even ( = 53.8). Each sequential value will result in a larger heating system (higher first cost for the owner and possibly higher ongoing energy use). Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 What About Climate Change? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Likelihood of Climate Change? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Shifting Focus to Calculating (Estimating) Design Heat Loss Starting with above-ground envelope components (for the time being) now later Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Above-Ground Heat Loss Occurs through opaque and transparent assemblies: q = (U)(A)(Δt) sensible loss This equation is applied component-bycomponent (since U and A differ for windows, walls, doors, roofs) Any design action that will reduce U, A, or Δt will reduce design heat loss, reduce heating system size (first cost), and reduce energy usage (saving resources and reducing operating costs if an active system is required) q = heat flow; U = overall coefficient of heat transfer; A = surface area of assembly; Δt = temperature difference across assembly Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Wall Assembly Example calculate the U-factor of a wall by adding up the R-values of the wall components and inverting the sum Components (between framing) R value Outside air film, winter wind 15 mph R = 0.17 Wood siding, 0.5 x 8 lapped R = 0.81 Sheathing, 0.5 thick R = 1.32 Mineral fiber batt insulation 5.5 R = 21.0 Gypsum wall board R = 0.45 Inside air film R = 0.68 R for total assembly R total 24.4 U = 1 / 24.4 = 0.04 U-factor = 1/R tot majority of resistance, this pattern is typical Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Above-Ground Heat Loss Also occurs as a result of infiltration (air leakage) through gaps in an assembly: q = (cfm)(1.1)(δt) sensible loss Estimating infiltration rate (cfm) is the trick Any design action that will reduce cfm (infiltration) or Δt will reduce design heat loss, reduce heating system size (first cost), and reduce energy usage (conserving resources and reducing operating costs if an active system is required) q = heat flow; cfm = infiltration rate (cubic feet of air per minute); 1.1 = unit conversion factor; Δt = temperature difference across assembly Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Residential Infiltration Sources Walls: can have substantial air leaks due to electrical outlets, doors, windows, plumbing and dryer vents, sill connections, window jambs, etc. Ceilings: somewhat less leaky than walls, but may involve recessed lighting, electrical boxes, attic openings Fireplaces: leakage varies greatly with state of the chimney (open or closed damper), framing layout, combustion air approach Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Infiltration Opportunities we can t see air, but can see the temperature effects of air flow (infiltration) by using an IR camera door seal leakage kitchen exhaust fan (backdrafting when off) left: right: Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Infiltration Opportunities via the visible spectrum via the IR spectrum Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Infiltration Opportunities weak links in the insulation (serving as an air barrier) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Estimating Infiltration (natural air exchange) air changes per hour (cu ft / hr) / 60 = cu ft / min [cfm] some rough math: at 0.5 ACPH with a 1000 sq ft house ( 10,000 cu ft); infiltration = (0.5)(10,000) / (60) = 83 cfm {an 8 x10 cube of cold air every minute} Btuh, say = (83)(1.1)(70-10 deg) = 5,478 {equivalent to 16 at 100-watt lamps} Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Measuring Infiltration estimating infiltration during design is as much an art as a science; measuring actual infiltration for a POE is fairly easy a blower door is used to pressurize a building, with the required fan speed indicating the leakiness of the building Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14