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Proceedings of the ASME 2017 International Mechanical Engineering Congress and Exposition IMECE2017

November 3-9, 2017, Tampa, Florida, USA

IMECE2017-70551

THE POTENTIAL FOR THERMAL WASTE ENERGY RECOVERY IN INDUSTRIAL KITCHENS

A. P. Wemhoff, T. Dai, A. S. Fleischer Department of Mechanical Engineering

Villanova University Villanova, PA, USA

ABSTRACT Industrial kitchens consume significant amounts of energy,

largely in the form of heat production by cooking and cleaning

equipment, which requires removal by the facility’s heating,

ventilating, and air conditioning (HVAC) system. One potential

means to improve the energy efficiency of industrial kitchens lies

in the use of waste energy recovery of hot wastewater from an

industrial-scale dishwasher. Examination of an on-campus

dining facility suggests that waste heat recovery can occur at the

facility gas hot water heater (HWH) and the dishwasher electric

hot water booster (HWB). This study suggests that waste heat

recovery is more financially viable in existing construction at the

electric HWB, despite yielding less recovered heat than the gas

HWH. A payback period of approximately two years is

calculated for the installation of a 146 kW shell-and-tube heat

exchanger. The corresponding annual source pollution reduction

is approximately 13 kg of SO2, 6.5 kg of NOx, and 6.5 metric

tons of CO2. However, new construction projects in similar

building configurations could also include HWH heat recovery,

resulting in a similar payback period but with more substantial

annual source pollution reduction values: 14 kg of SO2, 33 kg of

NOx, and 38 metric tons of CO2.

NOMENCLATURE

𝐴 Fluid temperature correction factor,

dimensionless

𝐵 Fluid flow correction factor, dimensionless

𝐶 Cost, dollars

𝑐𝑝 Specific heat capacity, J/kg K

𝐹𝑑 Daily activity, s/day

𝐹𝑓 Fluid density correction factor, dimensionless

𝐹𝑌 Yearly activity, days/yr

𝑚 Exponent used in cost estimation,

dimensionless

�̇� Mass flow rate, kg/s

𝑃 Payback, yr

𝑄 Heat, J

�̇� Heat flow, W

𝑇 Temperature, °C

�̇� Volumetric flow rate, m3/s

𝜀 Heat exchanger effectiveness, dimensionless

𝜌 Density, kg/m3

Subscripts:

c Cold

elec Electricity

gas Natural gas

h Hot

HWB Hot water booster

HWH Hot water heater

HX Heat exchanger

main Maintenance

r Reference

util Utility

0 Nominal value

INTRODUCTION Waste energy recovery is a well-known, simple means to

reduce the environmental impact of buildings, in particular their

heating, ventilating, and air conditioning (HVAC) systems.

While the majority of studies have focused on commercial

buildings, some specialized building types have recently been

examined. For example, the potential for waste energy recovery

in data centers has been examined by numerous researchers,

where applications have ranged from domestic hot water heating

to enhanced cooling via absorption refrigeration, to power

generation via an organic Rankine cycle [1].

One class of buildings that has not been thoroughly

investigated for waste heat recovery potential are industrial

kitchens, notably dining facilities seen in colleges and

universities, corporate campuses, hospitals, military bases, and

K-12 schools. The Energy Information Administration (EIA) has


shown that 380,000 food service facilities exist in the United

States [2], employing 3.4 million workers. While many of these

facilities are commercial restaurants, many of them are industrial

kitchens. In either case, the facility will nearly always contain an

industrial dishwasher, resulting in the potential for waste heat

recovery.

Several past studies have examined waste heat recovery

from dishwashers. De Paepe et al. [3] designed a heat recovery

system for a household dishwasher. They built a prototype and

validated the design with experiments. They achieved a 6-13

year payback for their system. Persson [4] developed and

verified simulation models for heat recovery for a dishwasher

and a washing machine connected within the same hot water

circuit. This work used a heat exchanger built into the machine.

Bengtsson [5] added a heat pump system and an energy storage

unit filled with water to a conventional dishwasher. Their heat

pump system reduced electricity consumption by 24%, with the

same operating time and temperatures.

Other studies have examined waste heat recovery in a

kitchen in a more general sense. Wang et al. [6] proposed a

system for waste heat recovery of kitchen exhaust air to

supplement ground-coupled heat pump systems in cold climates.

Onyango et al. [7] examined waste heat recovery in commercial

kitchens in Northern Ireland. They concluded that compact heat

exchangers could be effective at waste heat recovery through

retrofitting existing systems.

Additional studies exist that explore waste heat recovery

from hot wastewater in a more general sense. Meggers and

Leibundgut [8] built a heat recovery tank that accepts outgoing

warm wastewater into a heat pump for hot water waste heat

recovery. They found an average annual coefficient of

performance (COP) of 6.0. Shen et al. [9] operated a wastewater

source heat pump for 30 days to recover heat from wastewater

from a bathroom. The recovered heat was used to preheat

bathwater supply. The COP for the heat pump was 2.3-3.5.

Finally, Ramadan et al. [10] proposed a generalized calculation

procedure for drain heat recovery systems. Their approach can

be used to provide preliminary analysis of the viability of waste

heat recovery using basic experimental data.

The above studies provide general guidance on waste heat

recovery for a variety of systems, and the study discussed here

adds to the literature by exploring the relationship between waste

heat recovery location, source pollution reduction, and payback

period in a facility containing a gas hot water heater (HWH) and

an industrial dishwasher containing an electric hot water booster

(HWB). The results from this study indicate which industrial

kitchen facilities should be targeted for optimal waste energy

recovery in both source pollution reduction and financial

viability.

METHOD This study considers waste heat recovery in Donahue Hall,

an on-campus dining hall located on the Villanova University

campus. The facility was chosen since its single purpose is in

food service, and other on-campus dining facilities are multi-use.

Donahue Hall contains a gas-fired hot water heater (HWH) to

supply hot water to all equipment within the building, including

an industrial dishwasher. The dishwasher contains a separate

electric hot water booster (HWB) that increases the temperature

of the inlet hot water to improve sanitation during the

dishwashing process.

The study features four different categories of calculations:

1. Facility calculations to determine the dishwasher use

and energy consumption.

2. Heat exchanger calculations to determine performance

information for various heat exchanger sizes.

3. Environmental impact calculations to correlate energy

savings to source pollution reduction.

4. Financial calculations to determine the payback period

associated with evaluating each scenario. The payback

period is used to provide a recommended waste heat

recovery strategy.

Each of the above categories is now described in detail.

Facility Calculations

The goal of this analysis is to estimate the amount of source

pollution reduction that could be achieved using waste heat

recovery in Donahue Hall. Here, two possible arrangements are

considered:

1. Waste heat is recovered in the cold water supply line

for the gas-fired HWH supporting the entire facility.

2. Waste heat is recovered in the hot water supply line

leading into the electric HWB. The HWB is used to

increase the water temperature for standard dishwasher

functionality.

Figure 1 describes the system of interest to this study. The

dishwasher model for this study is UC-CW8-WS-4T from

Champion Industries. Cold (ambient) water enters the building

at a temperature 𝑇1 and volume flow rate �̇�𝐻𝑊𝐻. This water is

heated through the gas HWH to a fixed temperature 𝑇2. A portion

of the hot water, �̇�𝐻𝑊𝐵, is then supplied to the dishwasher. The

hot water enters the electric HWB at the dishwasher at 𝑇3, which

is slightly below 𝑇2 due to losses in transit. The electric HWB

then increases the water temperature to a fixed temperature 𝑇4,

and the wastewater leaves the dishwasher at a temperature 𝑇5.

The wastewater then exits the facility at a slightly reduced

temperature 𝑇6 due to losses in transit and mixing with other

wastewater. The leaving wastewater volumetric flow rate is

approximated as �̇�𝐻𝑊𝐻. Therefore, two locations are seen for

waste heat recovery: at the HWH inlet and the HWB inlet. The

waste heat recovered at the HWH inlet is

�̇�𝐻𝑊𝐻 = 𝜀𝐻𝑊𝐻�̇�𝐻𝑊𝐻𝑐𝑝(𝑇5 − 𝑇1) (1)

where 𝜀 is the heat exchanger effectiveness, and �̇� and 𝑐𝑝 are the

mass flow rate and specific heat capacity of water, respectively.

The mass and volumetric flow rates are related as

�̇� = 𝜌�̇� (2)

where a water mass density of 𝜌 = 1000 kg/m3 is used in this

study. The waste heat recovered at the HWB inlet is

�̇�𝐻𝑊𝐵 = 𝜀𝐻𝑊𝐵�̇�𝐻𝑊𝐵𝑐𝑝(𝑇4 − 𝑇3) (3)


If both heat recovery mechanisms are used, then a new

temperature 𝑇6′ is used for HWH waste heat recovery:

𝑇6′ = 𝑇6 −

�̇�𝐻𝑊𝐵

�̇�𝐻𝑊𝐵𝑐𝑝 (4)

In other words, the loss of thermal energy in the wastewater is

outside of possible HWB waste heat recovery and is assumed to

be constant.

Table 1 provides the values of the temperatures and flow

rates for the test facility. The hot water flowrate in the dishwasher

is 225 gph (2.37 × 10−4 m3/s) per drawings from Facilities

Management. Likewise, the cold water supply flowrate is set as

the hot water heater recovery rate of 840 gph (8.84 × 10−4 m3/s)

per drawings from Facilities Management. The wastewater

exiting the dishwasher is 150°F (66°C) per Villanova Dining

Services. The cold water supply temperature is assumed to be

50°F (10°C). The HWB is used to raise the dishwasher rinse

temperature to 180°F (82°C) per the dishwasher manufacturer

[11]. The hot water heater is assumed to provide a standard

140°F (60°C) outlet temperature. If a 10°F drop in temperature

is assumed for the hot water transit to and from the dishwasher,

then the inlet to the hot water booster is at 130°F (54°C) and the

outlet wastewater from the facility is 140°F (60°C).

Figure 1. General schematic of heat recovery options in the test

facility. DISH and HX refer to dishwasher and heat exchanger,

respectively.

The annual waste energy recovery for the facility is

estimated as

𝑄𝑌 = (�̇�𝐻𝑊𝐻 + �̇�𝐻𝑊𝐵)𝐹𝑑𝐹𝑌 (5)

where 𝐹𝑑 is the number of seconds per day that the dishwasher

is on, and 𝐹𝑌 is the number of days per year that the industrial

kitchen is active. It is assumed that the dishwasher runs

approximately the same amount of time per day that the facility

is open. The facility is open year-round except during the

summer break, so 𝐹𝑌 = 300 days/yr. The dishwasher is run an

average of 13.4 hours per day per Villanova Dining Services, or

the entire active period of the facility. Therefore 𝐹𝑑 = 4.82 ×104 s/day.

Table 1. Values of System Temperatures and Flow Rates Without

Heat Recovery

Parameter Value

𝑇1 50°F (10°C)

𝑇2 140°F (60°C)

𝑇3 130°F (54°C)

𝑇4 180°F (82°C)

𝑇5 150°F (66°C)

𝑇6 140°F (60°C)

�̇�𝐻𝑊𝐻 840 gph (8.84×10-4 m3/s)

�̇�𝐻𝑊𝐵 225 gph (2.37×10-4 m3/s)

Heat Exchanger Calculations

The analysis is centered around the use of B series heat

exchangers from Advanced Industrial Components Incorporated.

These straight shell-and-tube heat exchangers, shown in Fig. 2,

were chosen based on available pricing and performance

information from the vendor. It should be noted that the vendor

provides sanitary heat exchangers that provide extra preventive

measures to prevent the possibility of mixing of fluid streams,

but the sanitary heat exchangers are prohibitively expense for the

application used here [12].

The calculation scheme provided by the vendor [13] differs

from conventional heat exchanger analysis. The governing

equation for analyzing the heat flow �̇� by a heat exchanger is

�̇� = �̇�0𝐴𝐹𝑓,ℎ𝐹𝑓,𝑐√𝐵ℎ𝐵𝑐 (6)

where �̇�0 is the nominal heat flow, 𝐴 is a fluid temperature

correction factor, 𝐹𝑓 is a fluid density correction factor, and 𝐵 is

a fluid flow correction factor. The nominal heat flow is used in

the study to depict the size of the heat exchanger since UA values

are not provided. The subscripts 𝑐 and ℎ represent the cold and

hot fluid streams, respectively. The fluid temperature correction

factor is calculated as

𝐴 = 1.5Δ𝑇 + 10 (7)

where Δ𝑇 = 𝑇ℎ,𝑖 − 𝑇𝑐,𝑖 is the inlet fluid temperature difference.

The fluid density correction factor is tabulated for specific fluids

but can be generalized for water and mixtures of as

𝐹𝑓(𝛾) ≈ 0.01[1 − 2.89(𝛾 − 1)], 1 ≤ 𝛾 ≤ 1.06 (8)

where 𝛾 is the specific gravity of the fluid using water as the

reference density. Finally, the fluid flow correction factor is

given as

HWH

�̇�𝐻𝑊𝐻 𝑇1

To other

sinks

HWB

�̇�𝐻𝑊𝐵

𝑇2

𝑇3

𝑇4

𝑇6 or 𝑇6′

HX location for HWH

heat recovery

HX location for

HWB heat recovery

From other

sources

�̇�𝐻𝑊𝐻

DISH

𝑇5


𝐵 = 98.72 (�̇�

�̇�0) (9)

where �̇�0 is the nominal volumetric flow rate. It should be noted

that �̇�0 is unique for both fluid streams in each heat exchanger.

Values of �̇�0, �̇�𝑐,0, and �̇�ℎ,0 are provided in Table 2.

Figure 2. Heat exchanger model used in this study [13].

Table 2. Characteristics of Available Heat Exchangers [13]

Model �̇�𝟎, kW �̇�𝟎,𝒉, L/min �̇�𝟎,𝒄, L/min

B-45 13 23 150

B-70 20 25 170

B-130 38 27 200

B-180 53 30 210

B-250 73 35 270

B-300 88 40 300

B-400 117 46 342

B-500 146 55 360

B-1000 293 95 705

Environmental Calculations

The environmental and financial impact stems from the

savings in either (1) natural gas combustion associated with the

facility gas HWH, or (2) fossil fuel consumption in the

generation of electricity for the dishwasher electric HWB. The

three primary areas considered in the calculations are SO2

reduction, NOx reduction, and CO2 reduction.

The estimated source pollution reduction stems from the

fraction of statewide electric production. Since the power

sources vary widely by region, it is assumed that the power

source for electricity in the facility may be roughly approximated

by the statewide power production portfolio. Available

information from the Energy Information Administration (EIA)

[14]–[16] states that 38% of Pennsylvania (PA) statewide electric

power production in 2015 stemmed from nuclear fuel, 30% from

coal, 28% from natural gas, and the remaining 4% from other

sources. Nuclear energy has essentially zero emissions in the

categories considered in this study, and the majority of the

remaining sources are from renewables (e.g., wind and solar).

Therefore, it can be reasonably estimated that the source

pollution examined here is dominated by coal and natural gas

emissions.

Table 3 provides the source pollution from electricity

generation. The EIA data includes the total amount of statewide

electricity generation (in MWh) produced using each type of

fuel, along with their corresponding emissions in each of the

categories of interest to this study. The source pollution for each

kWh of electric consumption is approximated as a weighted

average of source pollution from the various fuel sources.

Table 3. Environmental Impact for Various Electric Power

Production Methods [14]–[16]

Method Coal Nat.

Gas

Other PA

Avg.

% of overall PA

production (kWh)

30 28 42 100

𝑆𝑆𝑂2, 10-4 kg/kWh 29.0 0.02 ~0 8.71

𝑆𝑁𝑂𝑥, 10-4 kg/kWh 12.7 1.25 ~0 4.16

𝑆𝐶𝑂2, 10-1 kg/kWh 9.86 4.23 ~0 4.14

Emissions data for direct natural gas combustion in the

facility hot water heater were calculated based on the average

heat value of natural gas and the produced pollutant per volume

of natural gas. This is required since the values shown in Table 3

inherently incorporate the efficiency of the power plant and

therefore cannot be reliable for direct combustion for purposes

of heating water. Table 4 provides the values of the parameters,

which allows for the calculation of the source pollution reduction

through reducing the natural gas consumption in the gas-fired hot

water heater.

Table 4. Source Pollution Due to Natural Gas Combustion [17]

Pollutant SO2 NOx CO2

Emission

(kg pollutant / m3 gas)

9.6×10-6 1.6×10-3 1.92

Emission1

(kg pollutant / J)

2.5×10-13 4.2×10-11 5.1×10-8

Notes - 2 - 1Assume a heat value of 1,020 Btu/scf 2Assume an emission factor of 100 lb/106 scf typical for

small or residential boilers

Financial Calculations

Cost information of the available heat exchangers was

derived based on the pricing of two heat exchangers by the

vendor. Following the estimate that the price of equipment

follows a power-law relation according to its primary

performance indicator as suggested in Burmeister [18],

𝐶𝐻𝑋 = 𝐶𝐻𝑋,𝑟 (�̇�0

�̇�0,𝑟)

𝑚

(10)

where the heat exchanger cost 𝐶𝐻𝑋 is calculated based on a

known reference heat exchanger cost 𝐶𝐻𝑋,𝑟 and its associated

nominal heat flow �̇�0,𝑟. Since the vendor provided the pricing for


two heat exchangers, the exponent 𝑚 in Eq. (2) was calculated

using the relation

𝑚 = ln (𝐶1

𝐶2) / ln (

�̇�0,1

�̇�0,2) (11)

where the subscripts identify each of the two heat exchangers.

The first heat exchanger was then chosen as the reference heat

exchanger, i.e. 𝐶𝐻𝑋,𝑟 = 𝐶𝐻𝑋,1 = $803 and �̇�0,𝑟 = �̇�0,1 = 53 kW.

The calculated exponent is 𝑚 = 0.356, which is below the value

of ~0.7 for larger, more expensive shell-and-tube heat

exchangers [19], [20].

Applying heat recovery at the HWH provides the advantage

of a larger inlet temperature difference, whereas the HWB

provides a more feasible retrofit operation. To quantify the

differences in each method, then waste energy recovery for new

construction and at the HWB will assume a standard labor and

installation cost of 100% of the equipment price [18], whereas a

retrofit at the HWH for an existing facility will have an assumed

cost multiplier of 300%. The reason for these numbers is the cost

and viability of routing sanitary and supply piping through the

heat exchanger. Changes to the supply piping is fairly simple

since the portion of piping considered is already exposed in the

mechanical room. However, the sanitary piping, which currently

connects to the sanitary main pipe, would need significant

rerouting to the mechanical room. Furthermore, this approach

would require core drilling of the existing concrete and the

addition of several feet of sanitary piping. Implementation of

waste heat recovery on the HWB is straightforward, meaning

that a 100% cost multiplier is warranted. Annual maintenance is

approximated at 20% of the total installed cost of the heat

exchanger.

Finally, the utility costs are $0.29/CCF for natural gas and

$0.10 per kWh of electricity per the local utility. Applying the

heat value in Table 4 for natural gas yields electric and natural

gas costs of 𝐶𝑒𝑙𝑒𝑐 = $27.8/GJ and 𝐶𝑔𝑎𝑠 = $2.69/GJ,

respectively. These values are used in payback calculation

estimates following

𝑃 =𝐶𝐻𝑋

�̇�𝑌𝐶𝑢𝑡𝑖𝑙−𝐶𝑚𝑎𝑖𝑛 (12)

where 𝐶𝑢𝑡𝑖𝑙 is equal to either 𝐶𝑒𝑙𝑒𝑐 or 𝐶𝑔𝑎𝑠, depending on where

the waste heat is recovered; and 𝐶𝑚𝑎𝑖𝑛 is the annual maintenance

cost.

RESULTS

Figure 3 provides the calculated heat recovery for each of

the heat exchanger sizes associated with the two waste heat

recovery scenarios (facility gas HWH and dishwasher electric

HWB). The figure clearly shows that the facility gas hot water

heater provides more heat recovery potential than the dishwasher

electric hot water booster. The reasons for this are twofold: the

gas hot water heater contains a larger inlet fluid temperature

difference (50°C vs. 11°C), and the gas hot water heater has a

nearly fourfold larger fluid flow rate. Furthermore, the larger

heat exchanger surface area associated with the larger nominal

heat exchanger sizes correspond to enhanced heat exchange. One

can see that the benefit from increasing the heat exchanger size

relaxes around the 146 kW nominal size for the gas HWH and

the 53 kW nominal size for the electric HWB, which is related to

the difference in flow rates in the respective heat exchange

scenarios.

Figure 3. Calculated heat recovery for different waste energy

recovery strategies.

Figure 3 gives the impression that a heat recovery strategy

that focuses on the gas HWH is much more financially viable

because of its larger heat recovery. However, further

investigation shows that waste energy recovery at the electric

HWB provides a comparable payback period in new

construction, and a shorter payback period in retrofitted

construction. Figure 4 shows the calculated payback period for

both of the scenarios, where the HWH payback period is

calculated for both new and retrofitted construction. The figure

clearly shows that the HWH under new construction and HWB

constitute the lowest payback periods, primarily due to the fact

that the cost of electricity, per Joule, from the utility is an order

of magnitude larger than that for natural gas. In general, all three

curves contain a minimum point at the 146 kW heat exchanger

because at low flow rates the heat recovery rate is too low, and

at too large flow rates the maintenance and upfront costs are too

high. The minimum calculated payback period is 1.7 years for

the 146 kW nominal heat exchanger associated with the gas

HWH in new construction, and 2.1 years for the same heat

exchanger size associated with the electric HWB.

Figures 5-7 provide the source pollution reduction

associated with individual electric HWB and gas HWH heat

recovery. The figures show that electric HWB heat recovery

results in much more SO2 savings than gas HWH heat recovery.

This is due to the low SO2 emissions associated with natural gas

combustion compared to the contribution of coal combustion in

electric production. However, gas HWH heat recovery provides

more NOx and CO2 source pollution reduction since the amount

of recovered heat with the gas HWH recovery overwhelms the

lower emissions associated with natural gas combustion

compared to electric production. The point of minimum payback

(gas HWH at 146 kW) is associated with an annual source

pollution reduction of 0.2 kg SO2, 28 kg NOx, and 34 metric tons

of CO2. For existing construction, the point of minimum payback


provides a source pollution reduction of 13 kg SO2, 6.5 kg NOx,

and 6.5 metric tons of CO2. Therefore, HWB heat recovery

provides more modest gains in source pollution reduction except

for SO2.

Figure 4. Calculated payback for different waste energy

recovery scenarios.

Figure 5. Calculated SO2 source pollution reduction for different

waste energy recovery strategies.

Figure 6. Calculated NOx source pollution reduction for

different waste energy recovery strategies.

Figure 4 shows a similar payback period for HWB heat

recovery and new construction HWH heat recovery. Therefore,

it is prudent to examine which combination of heat exchangers

in both waste recovery strategies yields the optimal payback

period. In order to achieve this the nine discrete sizes in Table 2

were interpolated to form contour plots consisting of a 50x50

grid, and then the 9x9 available sizes were mapped onto the plot

to identify the optimal size combination. The nominal hot and

cold water flowrates in Table 2 were interpolated for

intermediate �̇�0 values using spline curve fits.

Figure 7. Calculated CO2 source pollution reduction for different

waste energy recovery strategies.

Figures 8-11 provide the total heat recovery rate, SO2

reduction, NOx reduction, and CO2 reduction, respectively, by

various combinations of heat exchanger sizes when both HWB

and HWH heat recovery is implemented. Figure 8 shows that the

HWH heat recovery dominates, as expected per Fig. 3, although

the presence of HWB heat recovery shows an influence for a

combination of large HWB and HWH heat exchanger sizes.

Figure 9 shows that the SO2 source pollution reduction is

dominated by the HWB heat recovery, as expected per Fig. 5.

Finally, Figs. 10 and 11 shows that the NOx and CO2 source

pollution reduction are consistent with the overall heat recovery

in Fig. 8 and the individual source pollution reduction

contributions shown in Figs. 5 and 6.


Figure 8. Calculated total heat recovery, in kW, for various

combinations of heat exchanger sizes associated with both heat

recovery points in the system. The diamond markers indicate

available size combinations.

Figure 9. Calculated annual SO2 source pollution reduction, in

kg, for various combinations of heat exchanger sizes associated

with both heat recovery points in the system. The diamond

markers indicate available size combinations.

Figures 12 and 13 depict the payback period for both new

and retrofitted construction scenarios. As expected, the

retrofitted minimum payback period (3.6 years) is larger than

that for new construction (2.0 years). The location of minimum

payback for new construction occurs where both the electric

HWB heat exchanger and the gas HWH heat exchangers have a

nominal size of 146 kW. Choosing this combination results in an

additional annual source pollution reduction, compared to gas

HWH heat recovery only, of approximately 13.5 kg SO2, 5 kg

NOx, and 4 metric tons of CO2.

Figure 10. Calculated annual NOx source pollution reduction, in

kg, for various combinations of heat exchanger sizes associated

with both heat recovery points in the system. The diamond

markers indicate available size combinations.

For retrofitted construction, the optimal point is located at

146 kW and 53 kW heat exchangers for the HWB and HWH heat

recovery, respectively. This result suggests that the minimum

payback period for a system with multiple waste heat recovery

mechanisms may not coincide with the minimum payback point

for each heat exchanger size for independent waste heat recovery

(Fig. 4). Finally, Figs. 12 and 13 show a slightly different contour

pattern for small HWH heat exchangers and large HWB heat

exchangers since the retrofitted HWH construction results in

larger upfront and maintenance costs. When these added

expenditures are lifted, then larger heat exchangers become more

advantageous. The result is that the minimum payback period

point is shifted upwards for new construction compared to

retrofitted construction.

Figure 11. Calculated annual CO2 source pollution reduction, in

metric tons, for various combinations of heat exchanger sizes

associated with both heat recovery points in the system. The

diamond markers indicate available size combinations.


Figure 12. Calculated payback for various combinations of heat

exchanger sizes associated with both heat recovery points in the

system, where HWH recovery is installed as new construction.

The diamond markers indicate available size combinations.

Figure 13. Calculated payback for various combinations of heat

exchanger sizes associated with both heat recovery points in the

system, where HWH recovery is installed as retrofitted

construction. The diamond markers indicate available size

combinations.

CONCLUDING REMARKS For new construction, combining gas HWH and electric

HWB heat recovery using 146 kW heat exchangers provides a

reasonable payback period (2.0 years) with the potential for

annual source pollution reduction in the order of 14 kg SO2, 33

kg NOx, and 38 metric tons of CO2. For existing construction, a

similar payback period is achievable using HWB heat recovery

only with a 146 kW heat exchanger, but the source pollution

savings are less significant (13 kg SO2, 6.5 kg NOx, and 6.5

metric tons of CO2). Therefore, the use of waste heat recovery in

industrial kitchen dishwashers is economically viable and can

have a much more significant environmental benefit in new

construction. This study indicates that waste heat recovery

should especially be focused on facility-level electric hot water

heaters due to the higher emissions associated with coal versus

natural gas combustion. Furthermore, the source of electric

production is key to source pollution reduction in these

scenarios: a facility whose electricity is generated at a coal power

plant will have much higher potential for source pollution

reduction and energy savings than one near a nuclear or

renewable energy plant.

ACKNOWLEDGEMENTS This research has been supported by a grant from the U. S.

Environmental Protection Agency’s Source Reduction

Assistance Grant Program. Assistance from Villanova Dining

Services and Facilities Management is greatly appreciated.

ADDENDUM The results of this study were presented on July 31, 2017 to

Villanova Dining Services, where it was discovered that the

HWB was gas-fed, not electric, which means that for retrofitted

construction any waste heat recovery for the HWB would have

little environmental impact and have a prohibitive payback

period. Therefore, no recommended changes were made for

waste energy recovery in Donahue Hall. However, the results of

this study have indicated a new location where HWH waste

energy recovery could take place: a restaurant is under

construction as part of a campus expansion project.

REFERENCES [1] K. Ebrahimi, G. F. Jones, and A. S. Fleischer, “A Review of

Data Center Cooling Technology, Operating Conditions and

the Corresponding Low-Grade Waste Heat Recovery

Opportunities,” Renew. Sustain. Energy Rev., p. submitted,

2013.

[2] U. S. Energy Information Administration, “Summary table:

total and medians of floorspace, number of workers, and

hours of operation, 2012,” EIA-PBA2, 2016.

[3] M. De Paepe, E. Theuns, S. Lenaers, and J. Van Loon, “Heat

recovery system for dishwashers,” Appl. Therm. Eng., vol.

23, no. 6, pp. 743–756, Apr. 2003.

[4] T. Persson, “Dishwasher and washing machine heated by a

hot water circulation loop,” Appl. Therm. Eng., vol. 27, no.

1, pp. 120–128, Jan. 2007.

[5] P. Bengtsson, J. Berghel, and R. Renström, “A household

dishwasher heated by a heat pump system using an energy

storage unit with water as the heat source,” Int. J. Refrig.,

vol. 49, pp. 19–27, 2014.

[6] K. Wang, N. Li, J. Peng, X. Wang, C. Wang, and M. Wang,

“A highly efficient solution for thermal compensation of

ground-coupled heat pump systems and waste heat recovery

of kitchen exhaust air,” Energy Build., vol. 138, pp. 499–

513, Mar. 2017.

[7] J. Onyango, C. McGeough, and E. A. Obonyo, “Waste to

worth: Evaluation of potential waste heat recovery system

within commercial kitchens in Northern Ireland,” J. Green

Build., vol. 7, no. 4, pp. 62–69, 2012.

[8] F. Meggers and H. Leibundgut, “The potential of

wastewater heat and exergy: Decentralized high-


temperature recovery with a heat pump,” Energy Build., vol.

43, no. 4, pp. 879–886, Apr. 2011.

[9] C. Shen, L. Yang, X. Wang, Y. Jiang, and Y. Yao, “Predictive

performance of a wastewater source heat pump using

artificial neural networks,” Build. Serv. Eng. Res. Technol.

Lond., vol. 36, no. 3, pp. 331–342, May 2015.

[10] M. Ramadan, T. lemenand, and M. Khaled, “Recovering

heat from hot drain water—Experimental evaluation,

parametric analysis and new calculation procedure,” Energy

Build., vol. 128, pp. 575–582, Sep. 2016.

[11] “Conversation with NEMA-Associates,” 2017.

[12] “Conversation with Otilia Fuentes, Advanced Industrial

Components, Inc.,” 2017.

[13] Advanced Industrial Components, Inc., “B Series Heat

Exchangers,” 2017.

[14] U. S. Energy Information Administration, “Annual Electric

Generator Report,” EIA-860, 2016.

[15] U. S. Energy Information Administration, “Annual Electric

Power Industry Report,” EIA-861, 2016.

[16] U. S. Energy Information Administration, “Power Plant

Operations Report,” EIA-923, 2016.

[17] U. S. Environmental Protection Agency, “Compilation of

Air Emission Factors,” AP-42, 1995.

[18] L. C. Burmeister, Elements of Thermal-Fluid System

Design. Upper Saddle River, NJ: Prentice Hall, 1998.

[19] D. R. Woods, S. J. Anderson, and S. L. Norman, “Evaluation

of capital cost data: Heat exchangers,” Can. J. Chem. Eng.,

vol. 54, no. 6, pp. 469–488, 1976.

[20] J. D. Kumana, “COST UPDATE ON SPECIALTY HEAT

EXCHANGERS.,” Chem. Eng. N. Y., vol. 91, no. 13, pp.

169–170, 172, 1984.

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