HVAC HEATING COOLING VENTILATION. Human Comfort Zone As humans we try to maintain a body temperature...

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HVACHEATING

COOLING

VENTILATION

Human Comfort Zone

As humans we try to maintain a body

temperature of 98.6° F– Three Mechanisms

• Heat generated within the body• Heat gained from surroundings• Heat lost to surroundings

Human Comfort Zone

We shiver to

generate heat

Human Comfort Zone

We sweat to

Give off heat

Human Comfort Zone

We get goose bumps

Human Comfort Zone

Blood Flow– Decreases to hands and feet in winter– Increase in summer to encourage heat loss

Thermal Neutrality

To be comfortable humans must loose heat at the same rate as it is produced or gained.

Factors Affecting Human Comfort

• Air temperature

• Air Speed

• Humidity

• Mean radiant temperature

Each has a direct influence on heat loss or gain to the human body

• Air Temperature - This affects temperature differences between the body and the surroundings, consequently affecting the rate of heat loss or gain by convection.

Air Speed - This affects the rate at which

the body loses heat by convection. – An air temperature of 35°F and a wind speed

of 20 miles/hour combine to give a wind chill temperature of 11.2°F.

– Air speed is also very important during summer when the body is trying to lose heat to maintain comfort.

Humidity - Affects the rate at which the

body loses heat by evaporation. During hot

weather, high humidity increases discomfort

by making it more difficult to evaporate

perspiration into the air.

Mean Radiant Temperature

• Mean Radiant Temperature' (MRT). This is defined as the temperature of a sphere at the point in question which would exchange no net radiation with the environment.

Mean Radiant Temperature (MRT) - MRT is the average surface temperature of the surroundings with which the body can exchange heat by radiant transfer.

Radiant heat transfer to and from the body is quite apparent when sitting near a fireplace (high MRT) or large cold window area (low MRT).

Mean Radiant Temperature

In general for every 1 degree F that the MRT drops, the air temperature must be raised about 1.4 degrees F to achieve comfort conditions.

How can you raise the MRT?• Close blinds and curtains • Solar Film on windows• Seal heat leaks

Comfort

• Comfort is achieved by either increasing the ambient temperature or by raising the mean radiant temperature of an environment.

• A higher radiant temperature means that people become comfortable with a lower ambient temperature and the reverse is also true.

Bioclimate Chart

Example 1

• Dry Bulb 73°

• Relative Humidity 50%

In the zone

Example 2

• Dry Bulb Temp. 78°

Example 2

• Dry Bulb Temp. 78°• Relative Humidity

• Requires a wind speed of 250 FPM

(250*60)/5280

MPH = 2.84

Example 3

• Dry Bulb Temp. = 50°F

Example 3

• Dry Bulb Temp. = 50°F

BTU/Hour = 250

Definitions

• Conduction A method by which heat is transferred from a warmer

substance to a cooler substance by molecular collisions. Direct contact.

• Convection A method by which heat is transferred by currents in a

liquid or gas.

• Radiation A method by which heat can be transferred through

objects and empty space. Electromagnetic.

Conduction Examples

• Liquid - Liquid - Pouring cold cream into coffee

• Liquid - Gas - Ocean and Atmosphere

• Gas - Gas – Cold and warm weather systems mixing

• Solid - Solid – Touch a hot pot on a stove

Conduction Rate Factors

• Contact Area

• Type of Material Cast Iron vs Stainless Steel

• Temperature Difference

• Distance heat must travel

Convection Examples

• In a closed room cool air will settle to the bottom while warm air will rise

• Bowl of soup – Hot liquid in the center moves to the cooler outside where it drops and is reheated at the center and the cycle continues.

• Warm air rising through a heat register

Radiation Examples

• The sun’s heat

• A bonfire

• Warm soil on a cool night

Radiation Rate Factors

• Surface area

• Type of material

• Temperature difference

More Radiation Terms

• Reflectance (or reflectivity) refers to the fraction of incoming radiant energy that is reflected from the surface. Reflectivity and emissivity are related and a low emittance is indicative of a highly reflective surface.

• For example, aluminum with an emittance of 0.03 has a reflectance of 0.97.

More Radiation Terms

• Emittance (or emissivity), refers to the ability of a material’s surface to give off radiant energy. All materials have emissivities ranging from zero to one. The lower the emittance of a material, the lower the heat radiated from its surface.

Emissivity or Emittance

Material Surface Emittance

Asphalt 0.90 - 0.98

Aluminum foil 0.03 – 0.05

Brick 0.93

Fiberglass 0.80 – 0.90+

Glass 0.95

Steel 0.12

Wood 0.90

R-Value

• R-Value is the measure of resistance to heat flow through the defined material. The higher the R-Value the less heat will transfer through the wall, making the system more energy efficient.

• U-Value –is the reciprocal of the R-Value

(1/R) and is a measure of the rate of heat loss

WINDOWS - 4 Ways to Evaluate

• U-FACTOR

• Solar Heat Gain Coefficient

• Visible Transmittance

• Air Leakage

U-FACTORU-FACTORThe rate of heat loss is indicated in terms of the U-Factor of a window assembly. The insulating value is indicated by the R-Value which is the inverse of the U-Value.

The lower the U-Value the greater a windows resistance to heat flow and the better the insulating value.

Solar Heat Gain COEFFICIENTThe SHGC is the fraction of incident solar radiation admitted through a window.

SHGC is expressed as a number between 0 and 1. The lower a windows solar heat gain coefficient, the less solar heat it transmits.

VISIBLE TRANSMITTANCEThe visible transmittance is an optical property that indicates the amount of visible light transmitted.

Theoretical values vary between 0 and 1, but most values are between 0.3 and 0.8

Air Leakage

Heat loss and gain occur by infiltration through cracks in the window assembly.

Air leakage is expressed in cubic feet of air passing through a square foot of window area.

.3 is recommended for Oregon

Low-E Windows

• Glass is coated with silver or tin oxide which allows visible light to pass through but reflects infrared heat radiation back into the room.– Reduces heat loss

• Allows visible light to pass through but reflects infrared heat radiation away from the room– Reduces heat gain

High number for cold climate. Low number for warm climates

The lower the number the better the insulating value

The best windows have air leakage rating between 0.1 and 0.6 cfm/ft.

Varies from 0 to 1.0 The higher the # the more light is transmitted.

Single-Glazed with Clear Glass

Single-Glazed with Bronze or Gray Tinted Glass

Double-Glazed with High-Solar-Gain Low-E Glass, Argon/Krypton Gas

Triple-Glazed** with Moderate-Solar-Gain Low-E Glass, Argon/Krypton Gas

Ventilation

• Multi Point Fan Systems– One fan located in the attic– Connects to baths and kitchen– Timed to run at high speed during high use

times such as morning (showers, bacon ) and evening.

– Xvent

Heat Recovery Ventilation

How it works• In the heating season the core transfers heat

from the outgoing, stale household air to preheat the incoming, fresh air.

• Cross-current sections, ensure the two air streams are always kept separate preventing the incoming fresh air from being contaminated by the outgoing stale air.

• During the air-conditioning season, the HRV reverses this process, removing some of the heat from the incoming air and transferring it to the outgoing air.

Ventilation

• Heat Recovery System - uses fans to maintain a low-velocity flow of fresh outdoor air into the building (incoming air stream) while exhausting out an equal amount of stale indoor air (exhaust air stream). Fresh air is supplied to all levels of the building while stale air is removed from areas with high levels of pollutants and moisture.

Ventilation

Heat Recovery System

Air Exchange - Expels stale, polluted indoor air and gaseous pollutants and continually exchanges them with a continuous flow of fresh, revitalized outdoor air to improve Indoor Air Quality.

Ventilation

Excess Humidity Control - Helps prevent uncontrolled excess humidity by expelling excess humidity from the air, thereby reducing the risk of window condensation, mildew and mold, which prevents structural damage and deterioration to your home.

Ventilation

• Heat Recovery Core - As warm air is expelled from your house, it warms the incoming cold, fresh air before it’s circulated throughout your home. The result is a constant supply of fresh air, no unpleasant drafts and greater home comfort.

• Sized to ventilate the entire house at a minimum of .35 air changes per hour.

• Minimum CFM requirement can be calculated as follows

• Determine square footage and multiply times ceiling height.

• Divide by 60 minutes• Multiply times .35 (minimum air changes)

HRV Calculation

Example• Determine square

footage and multiply times ceiling height.

• Divide by 60 minutes

• Multiply times .35 (minimum air changes)

• Calculate the minimum CFM for a home

with 2000SF main level, 1000SF second level and 750 SF finished basement

Note: Main and second level have 9 foot

ceilings and basement has 8 foot

ceiling.

Solution

3000 SF x 9’ = 27000

750 x 8’ = 6000

Total 33000

33000/60 = 550

.35 x 550 = 192.5 CFM

HEPA Filter

Energy Recovery Ventilators

How are HRV’s Installed?

Radiant Floor Heat

Three types

• Radiant Air Floors

• Electric Radiant Floors

• Hot Water (Hydronic)

Radiant Floor Heat

Types of installation

Wet Installations• Large thermal mass of a concrete slab floor • lightweight concrete over a wooden subfloor

Dry Installations Where the installer "sandwiches" the radiant floor tubing

between two layers of plywood or attaches the tubing under the finished floor or subfloor.

Radiant Floor Heat

Air Heated Radiant Floors Not recommended for residential applications

Electric Radiant Floors -

Electric Radiant Heat - Wet Installation

Wet Installation

Dry Installation

Hydronic Radiant Heat

Wet Installation

• PEX piping in Concrete (thick slab)

Wet Installation

• Thin Slab Application Gypcrete over plywd

Electric Toe Kick Heat

Toe Kick Electric Heat

Heat Pump and Furnace

Indoor Cooling Coil

Heat PumpFurnace

Air Cleaner

Thermostat

Heat Pump and Air Handler

Heat Pump

Air Handler

Air Cleaner

Thermostat

Air Conditioner and Furnace

Air Conditioner

Furnace

Indoor Cooling Coil

Thermostat

Air Cleaner

Air Conditioners and Air Handlers

Thermostat

Air Conditioner

Air Handler

Air Cleaner

Cooling

HVAC HEATING COOLING VENTILATION. Human Comfort Zone As humans we try to maintain a body temperature...

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