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HEAT RECLAIM WATER HEATING

Using Waste Heat from Refrigeration Systems to Heat Potable Water

Phil McConnell

Sr. Product Manager

Therma-Stor LLC – Madison, WI

SEMINAR SYNOPSIS

• Reclaiming waste heat from a refrigeration system and using it to heat water is a proven, effective energy saving strategy applicable in many facilities. This session will focus primarily on using waste heat from a refrigeration system to heat potable hot water. After a brief introduction, topics will include determining when to consider using a heat reclaim system, feasibility analysis, system design/component selection, installation details including controls, and performance verification. Different heat reclaim system components will be discussed and compared along with sizing and selection examples. Return on investment calculations will be presented and discussed.

AGENDA

• Introduction

• Criteria for application (when to use)

• Feasibility

• ROI

• System design

• Component options

• Sizing of components

• System design

• Controls

• Performance verification

HEAT RECLAIM INTRODUCTION

REFRIGERATION CYCLE

WHY WATER HEATING?

• Facility has refrigeration and uses hot water• The lower, the better!

• The higher, the better!

• High-grade heat from superheated gas works well for boosting water temperatures

• Desired final water temperature is higher than most other potential uses for reclaimed heat

• Both are good reasons for using desuperheaters for heating water• Potential for additional heat reclaim downstream

• Full condensing

• Refrigerant to air (secondary condenser)

BENEFITS OF HEAT RECLAIM

• Water heating savings

• Reduces fuel consumption needed to heat water

• Natural gas

• Electricity

• Reduces carbon footprint and emissions

• Reduces runtime on water heater

• Increases life cycle

BENEFITS OF HEAT RECLAIM

• Refrigeration benefits

• Increases compressor efficiency

• Approximately one percent per degree of reduction in condensing temperature

• Potential for effective increase in system capacity

• Reduced water use for

• Water cooled systems

• Evaporating condensers

• Reduced water treatment

CRITERIA FOR APPLICATION

When to use

ROI/Feasaiblity

CRITERIA FOR APPLICATION

• Refrigeration considerations

• Hot water considerations

• Logistics

REFRIGERATION CONSIDERATIONS

• Capacity

• Evaporator temperature

• Lower is better

• More high-grade heat

• More compressor runtime

• Refrigerant type

• Pressure drop (restriction) characteristics

• Discharge temperature

• Available superheat (head pressure)

HOT WATER CONSIDERATIONS

• Overall hot water demand

• Coincidental use

• Use water at the same time refrigeration system is running

• Cost of water heating fuel

LOGISTICAL CONSIDERATIONS

• Need to get the water and refrigerant close to each other

• Pipe refrigerant to water

• Plumb water to refrigerant

• Proximity of water heating system to refrigeration system

• Compressor

• Other facility related issues

• Freeze protection

• Structural issues

ROI - OVERVIEW

• How much does it cost to install

• How much can it save?

ROI - OVERVIEW

• How much does it cost to heat water

• Amount of energy used

• Value of energy used

• Fuel source and level of efficiency

• Electricity = 100%

• Gas = efficiency rating less scale/lime

• Don’t consider standby losses

• Calculate Btu’s and value of fuel

• Compare to cost of installation

• Consider additional benefits

ROI – BTU’S USED TO HEAT WATER

Example100 gallons X 8.33 pounds per gallon X 85 degree F rise = 70,806 BTUs divided by 60% efficiency = 118,008 BTUs to heat 100 gallons of water, 85 degrees F, with a 60% water heater efficiency.

Natural Gas118,008 BTUs to heat 100 gallons of water divided by 100,000 BTUs per therm X $1.00 per therm = $1.18 to heat 100 gallons, 85 degreesF, with a 60% water heater efficiency.

Electric78,672 BTUs to heat 100 gallons of water divided by 3413 BTUs per KWH X $.12 per KWH = $2.77 to heat 100 gallons of water, 85 degrees F, with a 90% water heater efficiency.

___ gallons X 8.33 pounds per gallon X ___ degree F rise = ___ BTUsdivided by ____% water heater efficiency = ____ BTUs

ROI – BTU’S USED TO HEAT WATER

• Easiest to estimate water use if there is no data

• Usually not a lot of data on hot water use

• Possible to measure hot water use to learn more

• Easiest to assume water use is constant

• We know it’s not

• Difficult to figure otherwise

• Make sure all parties are comfortable with the assumptions used to calculate the ROI

• Consider using a couple of calculations

• Highest/lowest water flow

• Largest/smallest compressor capacity

ROI – CALCULATION FORM

SYSTEM DESIGN

DESUPERHEATING WATER HEATERS

• Potable vs. non-potable

• Potable water heat exchanger

• Double-wall

• Vented

• UL listed

• Two basic styles

• Tank

• Non-tank

DOUBLE WALL CONSTRUCTION

DOUBLE WALL CONSTRUCTION

DESUPERHEATING WATER HEATERS – TANK STYLE

DESUPERHEATING WATER HEATERS – TANK STYLE

• Water storage tank with integrated heat exchanger

• Advantages

• No water pump required

• Lower power and maintenances

• Reduced scaling/liming potential

• Backup/booster heating optional

• Disadvantages

• Size

• Proximity to compressors

• Not outdoor rated

• Single size, multi-circuit

DESUPERHEATING WATER HEATERS – TANK STYLE

• Sizing

• Consider refrigeration system first

• Limited capacities available

• Too small = too restrictive

• Too large = condensing refrigerant

• Typically based on compressor capacity

• Then consider water heating system

• Try to maximize heat recovery within refrigeration parameters

• Evaluate potential contribution to total load

• ROI calculation

• Logistics

DESUPERHEATING WATER HEATERS – TANK STYLE

DESUPERHEATING WATER HEATERS – TANK STYLE

• Installation details

• Refrigerant

• Hot gas piped to desuperheater

• Warm gas piped to condenser

• Three way valve to control flow based on water temperature

• Water

• Cold water plumbed to inlet

• Warm water plumbed

• Facility

• Water heater

• Recirculation return to mid-port of tank

• Controls

• Aquastat

• Rack controller

DESUPERHEATING WATER HEATERS – TANK STYLE

DESUPERHEATING WATER HEATERS – TANK STYLE

DESUPERHEATING WATER HEATERS – TANK STYLE

• Installation details

• Refrigerant

• Hot gas piped to desuperheater

• Warm gas piped to condenser

• Three way valve to control flow based on water temperature

DESUPERHEATING WATER HEATERS – TANK STYLE

• Water

• Cold water plumbed to inlet

• Warm water plumbed

• Facility

• Water heater

• Recirculation return to mid-port of tank

• Controls

• Aquastat

• Rack controller

• Various sizes , multi-circuit

DESUPERHEATING WATER HEATERS – TANK STYLE

• Controls

• Pressure switch to cycle fan (small units)

• Water bleed valve (multi-circuit)

• Refrigerant 3-way valve is installed on the hot gas line, controlled by an aquastat

• When the water temperature is satisfied, the 3-way heat reclaim valve diverts the hot gas directly to the condenser.

DESUPERHEATING WATER HEATERS – TANK STYLE

DESUPERHEATING WATER HEATERS – NON-TANK

DESUPERHEATING WATER HEATERS – NON-TANK

DESUPERHEATING WATER HEATERS – NON-TANK

• Non-tank type

• Separate heat exchanger and water storage tank

• Advantages

• Small size

• Flexible application

• Outdoor possible (protect from freezing)

DESUPERHEATING WATER HEATERS – NON-TANK

• Disadvantages

• Water pump required

• Increased maintenance and cost

• Subject to scaling and liming

• Reduced efficiency over time

• Increased maintenance

• Multi-circuit units available

DESUPERHEATING WATER HEATERS – NON-TANK

• Sizing

• Multiple sizes available

• Selection based on refrigeration capacity and water flow

• Water heating system sizing

• Pump sizing

• Storage tank sizing

• ROI calculation

• Logistics

DESUPERHEATING WATER HEATERS – NON-TANK

• Installation details

• Refrigerant

• Hot gas piped to desuperheater

• Warm gas piped to condenser

• Three way valve to control flow based on water temperature (option)

DESUPERHEATING WATER HEATERS – NON-TANK

• Water

• Cold water plumbed to storage tank

• Cold water pumped trough desuperheater and back to tank

• Warm water plumbed

• Facility

• Water heater

• Recirculation return to mid-port of tank

• Controls

• Aquastat to control pump or three-way valve

• Pressure switch optional

DESUPERHEATING WATER HEATERS – NON-TANK

DESUPERHEATING WATER HEATERS – NON-TANK

DESUPERHEATING WATER HEATERS – TANK STYLE

• Controls

• A 3-way valve is installed on the hot gas line, controlled by an aquastat

• When the water temperature is satisfied, the 3-way heat reclaim valve diverts the hot gas directly to the condenser

• Pump control

DESUPERHEATING WATER HEATERS – NON-TANK

DESUPERHEATING WATER HEATERS – NON-TANK

DESIGN CONSIDERATIONS

SCALING POTENTIAL

SCALING POTENTIAL

• Scaling is a potential problem in desuperheaters when the secondary fluid is water, because the solubility of limestone (CaCO3) decreases with increasing temperature. The maximum water temperature should ideally not exceed 65-70°C (149-158 F) to avoid scaling problems. If the risk of scaling is increased by the use of hard water, etc., the use of co-current flow should be considered to reduce the risk of excessively high water temperatures.

SCALING POTENTIAL

SCALING AND EFFICIENCY

• Consequences of scaling/liming

• 1/16” scale requires 15% more fuel

• 1/8” scale requires 20% more fuel

• ¼” scale requires 39% more fuel

• 3/8” scale requires 55% more fuel

• ½” scale requires 70% more fuel

• Source: US Bureau of Statistics

VERIFYING PERFORMANCE

BTU METERS

DATA LOGGING

• Hot water use (gallons)

DATA LOGGING

• Hot water temperature and demand

DATA LOGGING

• Water heating system temperatures

DATA LOGGING

• System temperatures with flow

DATA LOGGING

• Gas water heater flue temperatures

DATA LOGGING

QUESTIONS?

THANK YOU!

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