Facilities management paper
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ZemkeCh9PPT.pptxHeating Systems
Chapter 9
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Air conditioning – definition
(it’s probably not what you thought it was)
…“the process of treating air so as to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the comfort requirements of the occupants of the conditioned space.”
Therefore, air conditioning includes both heating and cooling the air!
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Heat energy transfer
Always travels to where it is not – heat wants to achieve equilibrium
It will travel up, down, sideways
It will travel through space, air, walls, windows, furniture, bodies, and anything else it encounters
Two rooms next to each other, 1 colder than the other, air in both rooms will attempt to equalize the temperature in both rooms. The hotter air will move towards the cooler room.
For conditioned air, you can only add or remove heat. You do not introduce or remove cold air
1. Introducing science: Not really anything as “cold” just the absence of heat energy.
2. Heat energy can travel in any direction, unlike heated/hot/warmer air which always rises.
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Types of heat
Sensible heat
what you feel
does not account for humidity
dry-bulb temp
measured with a regular thermometer
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Types of heat
Latent heat
water vapor in the air combined with sensible heat
the results from an increase or decrease in the amount of moisture held by the air.
energy needed to cause a phase change without changing the actual temperature of a substance.
wet-bulb temp
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Relative humidity (rh) and the dew point
Air holds water vapor; warmer air can hold more water than cooler air
Relative humidity describes how much water vapor the air currently contains, as a percent of the total capacity at the current temperature
Air that is 70oF and at 50% relative humidity holds a lot more water than air that is 30oF that is also at 50% relative humidity
The dew point is when the air temperature:
reaches 100% relative humidity
is completely saturated
will cause water vapor to condense out of the air
Higher the dew point, the more humid it is, which will affect comfort
When you see/watch weather forecast and they mention Relative Humidity (RH) is 40%, that means the air is holding 40% of the total moisture it is capable of before dew/condensation forms.
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Condensation
The glass (beverage & ice) colder than room dew point, therefore, cannot hold as much water, point of saturation causing air to release moisture (condensation).
As the sun rises, temperatures increase, air becomes warmer and can hold more water.
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Types of heat transfer
Radiant
Conduction
Convection
Natural convection
Forced convection
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Radiant heat transfer
Movement of heat thru space
No direct contact between the heat source and the heated object
No mass is exchanged and no medium is required in the process of radiation.
Heat leaves one body and travels through the air to another, examples:
Sun
Body heat
Lighting
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Conduction heat transfer
Direct contact between two objects
Heat is transferred from warmer object to cooler one
The better the conductor, the more rapidly heat will be transferred.
When a substance is heated, particles gain more energy, and vibrate more, these molecules bump into nearby particles and transfer some of their energy to them.
Conduction in a kitchen: Using a broiler to cook meat, the meat is in direct contact with the broiler grate, heat from metal transfer into the meat.
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Convection heat transfer
The transfer of heat from one place to another by the movement of fluids. Usually the dominant form of heat transfer in liquids and gases.
Warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. Cooler liquid or gas then takes the place of the warmer areas which have risen higher, resulting in a continuous circulation pattern.
Examples:
Boiling water,
Atmosphere, warm air rises, cooler air takes its place
Heated fluid/gas is caused to move away from the source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes less dense, and rises. Hot water is likewise less dense than cold water and rises, causing convection currents which transport energy.
Cooking food: use of convection oven, radiant heat assisted by a fan moves heat around the food, reduces cooking time.
In a guest room or home good example is baseboard heat, heat transfer with the movement of air, naturally creating a circular pattern.
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Convection heat types
Natural convection
Forced convection
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Comfort zone for comfort air conditioning
Traditionally measured at the “breathing line”
Dry-bulb temperature: 68 – 78oF (20 – 25.5oC)
Humidity: 20% - 60%
Depending on:
Season
Activity in the space
Air movement
Attire of occupants in the space
Breathing line is approximately 5 ft above the floor
Would the type of activity help determine/dictate any pre-set temperatures?
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Thermostats
Mechanical
Digital
Mechanical thermostats: a. inexpensive, easy to install b. use bimetallic strips with different expansion properties (temp) c. loose calibration
Digital thermostats: a. use a sensor called a thermistor b. programable (days, times, etc.,)
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Heating “loads”
A heating load is an event or activity that requires us to add heat to the space
Internal heating loads – not too common in hospitality
Ex: adding heat to the audience seating area of an ice arena
External heating loads – very common
Ex: cold outdoor temperatures – heat from inside the building tries to escape to the outdoors; we need to turn the heat on to heat the space to a comfortable temperature
Internal heating load: freezers, coolers opening & closing, frozen food left out to thaw, very cold items/objects brought into the building
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Infiltration
Cold air enters building, exterior doors, poor seals, etc. Since heat moves to cold, infiltration is actually heat escaping through poor seals, cracks, opening/closing exterior doors.
Remember: Infiltration is heated air escaping the building
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Types of heating systems
Decentralized
Heat is created in a space, serving only that space or room
Electric baseboard
Electric radiant
PTAC units
“Package” units
Centralized
Heat is created in a central location, then transported throughout the building
Steam systems
Hydronic baseboard
Hydronic radiant
Fan-coil units
Air handling units
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Decentralized Systems
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Electric resistance heating
Decentralized systems: self-contained, no interface, connection with other building systems
Electric current across high resistance coil, generating heat
Examples: baseboard, portable, electric stove coils, sub-flooring radiant systems.
From an engineering prospective: least efficient
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Package terminal air conditioning unit (PTAC)
Smaller properties ≈ 200 rooms. Most common hotel HVAC system in North America
Easily maintained
Combined heating & cooling: heat pump w/electric strips
Noisy/loud
1. Electricity for both heating and cooling. 2. Easy to replace is necessary vs. time consuming & expensive repairs 3. No special skills to operate/install like centralized equipment
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Package unit
Larger spaces: meeting rooms, restaurants, public spaces
Like forced air systems: air across heated coil, distributed via air ducts
Heating commonly electric resistance
Not preferred or suitable for guest rooms
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Residential package unit & alternatives
Residential: roof or ground install
Split systems
Residential, smaller spaces
Mini-split systems
Tight spaces, specific space/use
Split systems: Commonly called forced air systems.
Mini-split: Commonly called ductless systems. Advantages?
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Decentralized pros and cons
Pros
Low material and installation costs
Usually easy to maintain
When a unit fails, it only affects one small area of the building
Cons
High energy costs (especially all-electric operation)
Noisy operation (PTACs)
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Radiant heat systems
Decentralized & centralized systems
Most commonly installed in floors
Items in contact with floor are heated providing secondary radiant heat
Considered sustainable
Outdoor applications
Electric radiant heat systems most common in bathrooms. Not extremely efficient for entire buildings/homes. One thought: your feet are warm your body is warm, reduced cost?
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Centralized Systems
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Centralized Heating Systems
Circulates steam or heating hot water (HHW)
Steam or HHW is generated in a single location; i.e., engine room, central plant, etc.
Steam delivered thru pipes or radiators
HHW circulated through pipes for hydronic baseboard, radiant floor, fan coil or air handling (AHU) units.
Chapter 6: HHW, quick review.
Boilers – large tanks that heat and store water. Indirect & direct contact: water either comes in direct contact with the heating source or contact with tubes (heating source inside tubes)
Fire-tube: a tank of water with pipes running through it; flames shoot through the pipes to heat the tank of water
Water-tube: a tank of fire has pipes running through it; water flows through the tubes to pick up heat from the fire
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Steam heat: Step 1- create steam
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Steam Heat
Water heated past boiling point, low-pressure steam
Piped to radiators
Not common in newer buildings
Hard to control heat/temp
On/off
Manual control
Radiator same temp as steam
Steam traps: trap/collect condensate from steam and return to boiler
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Heating Hot Water (HHW) systems “Hydronic”
Baseboard heating
Circulate hot water
Quiet, no fans
Conductive heating principles
Heating only
Hydronic = use of fluids
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Hydronic radiant systems
Commonly installed in floors, can be in walls
More efficient than electric resistance radiant heating
Entire buildings
Maintenance concerns
Maintenance issues: leaks, clogs, large areas under concrete. Flooring systems must be removed to repair.
Much more efficient than electric resistance radiant systems
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Radiant heat exterior applications
Cost is a consideration; however, is it worth preventing customers from slipping and falling, or shoveling snow? Personally, I don’t want to shovel snow anymore.
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All-water fan-coil and air handling systems
These centralized systems use heating hot water (HHW) and chilled water (CHW) to provide heating and/or cooling to the conditioned spaces
Small spaces deliver heating and cooling using a fan-coil unit
Larger paces deliver heating and cooling using an air handler
For heating, the HHW flows through a pipe (a.k.a., coil) inside the unit. A fan blows cold room air over the pipe. The air absorbs heat from the HHW in the pipe, providing warmer air to the space.
For cooling, the CHW flows through the coil. The warm room air is blown across the CHW coil; the CHW absorbs heat from the air. Cooler air is sent to the room.
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Fan-coil unit
Small units designed for small spaces, i.e., individual rooms. HHW no DHW is used. Called fan coil: coiled-up, lots of coils to maximize heat transfer, similar to a car radiator.
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Air handling unit (AHU)
Large spaces, some are big enough for people to stand in them! Design similar to fan coil units
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Centralized pros and cons
Pros
Often more energy-efficient than decentralized units
Usually quieter operation
Cons
If system fails, a large part of the property is affected
More expensive to purchase and install
More expensive to maintain
May require licensed personnel to operate
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Supply and return piping
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Supply and return piping
Supply pipes send HHW or CHW to the unit: fan coil unit(FCU) or air handling unit (AHU)
Return pipes send the water back to the boiler or chiller
HHW – which gave heat to the room’s air – returns to the boiler to pick up more heat
CHW – which picked up heat from the room’s air – returns to the refrigeration machine (chiller) to get rid of heat
We have three piping arrangements
Two-pipe
Three-pipe
Four-pipe
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HHW and CHW piping: 2 pipe
Two-pipe system – one supply pipe and one return pipe. The unit is supplied with either HHW or CHW; not both at the same time.
The room either gets heat or cooling
Most likely to cause customer complaints
Both Fan Coil Units (FCU) and Air Handling Units (AHU) use same type of piping systems. Do not be confused by the illustrations.
Customer cannot have both heat & cooling, challenging in transitional seasonal times (Oct-Dec) & (Apr-May) in LV.
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HHW and CHW piping: 3 pipe
Three-pipe system: the FCU has a HHW supply, a CHW supply, and a shared return line.
The room can receive heating or cooling; lukewarm water returns to the boiler and the chiller.
Least energy efficient of all piping systems
Returns water less than optimal for either heating or cooling. Want heated water to return as hot as possible and cooled water as cold as possible, saves energy.
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HHW and CHW piping: 4 pipe
Four-pipe system – one HHW supply, one CHW supply, one HHW return, and one CHW return
The room can get heating or cooling; the HHW returns to the boiler and CHW returns to the chiller without mixing
This creates good occupant thermal satisfaction while also returning water to the boiler or chiller with a lower difference in temperature (which is more energy efficient)
Most efficient and will provide guest with best comfort levels, ability to maintain desired temperature levels.
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Centralized heating systems safety
Pressure relief valves (PRV)
Licensed employees: > 15 psi
Equipment venting
Prevent carbon monoxide poisoning!
Carbon monoxide detectors
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Heating system maintenance
Scale – as covered in Chapter 6, mineral scale is the enemy of all water systems, particular as the water gets hotter
Chemically treated water to maintain pH and mineral content
Scale can cause tubes to leak & corrode: decrease efficiency, shorten life-cycle, failure
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Better maintenance = Better Efficiency
Energy efficiency = $, a little additional maintenance will increase profitability
Keep equipment clean: ductwork, pipes, coils
Insulate pipes & ductwork
Doors & windows: weather stripping, caulking, closers
Seal the building envelope
Replace windows
Change filters frequently. Static pressure will help determine on larger air handling units.
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Conservation Controls
Overhead fans
Setback thermostats, occupancy sensors
Revolving doors
Integrated PMS/FO systems –link occupancy sensors to the hotel’s front office systems
Keycard systems
EnergyStar certification for building energy performance
Revolving doors are more energy efficient, traps air in a isolated space. Integrated Property Management System and Front Office systems link check-in/out to room occupancy, can have pre-set/set back temps. Automatically turns on heat/cool upon check-in, then returns at check-out vs. housekeeping (variable depending on attendant, no guess work).
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New construction or renovation projects to save energy and improve comfort
Passive solar design
Solar water heating systems
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