CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

**4.1 INTRODUCTION** 

**........................................................................................................... 4­1** 

**4.2 SCREENED­OUT**  **TECHNOLOGIES............................................................................ 4­2**

**4.2.1 Water**  **Heaters....................................................................................................... 4­2** 

**4.2.1.1 Side­Arm**  **Heater (Gas**  **and Oil**  **Storage)**

**............................................... 4­2** 

**4.2.1.2 Flue Damper (Buoyancy Operated) (Gas Storage)............................... 4­3** 

**4.2.1.3 Directly Fired (Gas and Oil Storage).................................................... 4­3** 

**4.2.1.4 Condensing**  **Pulse Combustion**  **(Gas, Oil**  **Storage, and** 

**Instantaneous)**

**...................................................................................................... 4­3** 

**4.2.1.5 Advanced**  **Forms of**  **Insulation (Gas,**  **Electric, and**  **Oil Storage)** 

**.......... 4­4** 

**4.2.1.6 Thermophotovoltaic**  **and Thermoelectric**  **Generators (Gas,**  **Oil**

**Storage, and**  **Instantaneous)**

**................................................................................. 4­5** 

**4.2.1.7 U­Tube**  **Flue (Gas**  **and Oil**  **Storage)...................................................... 4­5**

**4.2.1.8 Reduced**  **Burner Size**  **(Slow Recovery)**  **(Gas, Oil**  **Storage, and** 

**Instantaneous)**

**...................................................................................................... 4­5** 

**4.2.1.9 Two­Phase**  **Thermosiphon (Gas**  **and Oil**  **Storage)**

**................................ 4­6** 

**4.2.1.10 CO**  **2 Heat Pump Water Heater (Electric Storage) ................................. 4­6** 

**4.2.2 Direct**  **Heating Equipment** 

**................................................................................... 4­6** 

**4.2.2.1 Increased**  **Heat Transfer**  **Coefficient (Fan**  **Wall, Gravity**  **Wall,**

**Floor, Room)........................................................................................................**  **4­7**

**4.2.2.2 Power**  **Burner (Fan**  **Wall, Gravity**  **Wall, Floor,**  **Room)**

**........................ 4­7** 

**4.2.2.3 Condensing**  **Pulse Combustion**  **(Fan Wall,**  **Gravity Wall,**  **Floor,**

**Room)**

**............................................................................................................... 4­8** 

**4.2.2.4 Improve**  **Fan or**  **Blower Motor**  **Efficiency (Fan**  **Wall).......................... 4­8** 

**4.2.3 Pool**  **Heaters......................................................................................................... 4­8**

**4.2.3.1 Condensing**  **Pulse Combustion** 

**............................................................. 4­9** 

**4.3 REMAINING**  **TECHNOLOGIES**

**................................................................................... 4­9** 

**4­ i** 4.1 INTRODUCTION

**This chapter**  **details the**  **screening analysis**  **that the**  **U.S. Department**  **of Energy** 

**(DOE) conducted**  **in support**  **of the**  **ongoing energy**  **conservation standards**  **rulemaking**

**for residential**  **water heaters,**  **direct heating**  **equipment (DHE),**  **and pool**  **heaters.**

**In the**  **market and**  **technology assessment**  **(MTA; chapter**  **3), DOE**  **presents an** 

**initial list**  **of technologies**  **manufacturers can**  **use to**  **improve the**  **energy efficiency**  **of**

**residential water**  **heaters, DHE,**  **and pool**  **heaters. The**  **purpose of**  **the screening**  **analysis is** 

**to evaluate**  **the technologies**  **that improve**  **product energy**  **efficiency to**  **determine which** 

**technologies DOE**  **should consider**  **further in**  **the rulemaking**  **analyses. DOE**  **consulted a** 

**range of**  **parties, including**  **industry and**  **technical experts**  **and others,**  **to develop**  **a list**  **of**

**technologies for**  **consideration. Some**  **of these**  **technologies can**  **reduce annual**  **energy**

**consumption of**  **products in**  **actual applications,**  **but may**  **not improve**  **the energy**  **factor**

**(EF), the**  **annual fuel**  **utilization efficiency**  **(AFUE), or**  **the thermal**  **efficiency of**  **water**

**heaters, DHE,**  **and pool**  **heaters, respectively.**  **The EF**  **of water**  **heaters is**  **measured using** 

**DOE’s test**  **procedure specified**  **in 10**  **Code of**  **Federal Regulations**  **(CFR) section**  **430**

**Subpart B,**  **Appendix E,**  Uniform Test Method for Measuring the Energy Consumption of

Water Heaters

**. The**  **AFUE of**  **DHE is**  **measured using**  **DOE’s test**  **procedure specified**  **in**

**10 CFR**  **430 Subpart**  **B, Appendix**  **O,** Uniform Test Method for Measuring the Energy

Consumption of Vented Home Heating Equipment

**. The**  **thermal efficiency**  **of pool**  **heaters**

**is measured**  **by the**  **American National**  **Standards Institute**  **(ANSI)** Standard for GasFired Pool Heaters **(ANSI Z21.65­1994),**  **which DOE**  **has incorporated**  **by reference**  **into**

**its regulations**  **at 10**  **CFR 430**  **Subpart B,**  **Appendix P.**  **DOE removed**  **from consideration** 

**those technologies**  **that do**  **not increase**  **EF, AFUE,**  **or thermal**  **efficiency per**  **these test** 

**procedures. DOE**  **evaluated the**  **remaining technologies**  **pursuant to**  **the criteria**  **in The** 

**Energy Policy**  **and Conservation**  **Act (EPCA),**  **as amended.**  **(42 U.S.C.**  **6311­6317)**

**Section 325(o)**  **of EPCA**  **establishes criteria**  **for prescribing**  **new or**  **amended**

**standards designed**  **to achieve**  **the maximum**  **improvement in**  **energy efficiency.** 

**Furthermore, EPCA**  **directs the**  **Secretary of**  **Energy to**  **determine whether**  **a standard**  **is**

**technologically feasible**  **and economically**  **justified. (42**  **U.S.C. 6295(o)(2)(A)(B))**  **In**

**view of**  **this requirement,**  **10 CFR**  **part 430,**  **subpart C,**  **appendix A,**  **4(a)(4) and**  **5(b)**

**guides DOE**  **in its**  **consideration and**  **promulgation of**  **new or**  **revised product**  **efficiency**

**standards. These**  **procedures elaborate**  **on the**  **statutory criteria**  **provided in**  **42 U.S.C.** 

**6295(o) and,**  **in part,**  **eliminate problematic**  **technologies early**  **in the**  **process of** 

**prescribing or**  **amending an**  **energy efficiency**  **standard. In**  **particular, DOE**  **determines**

**whether to**  **eliminate from**  **consideration any**  **technology that**  **presents unacceptable** 

**problems with**  **respect to**  **the following**  **criteria:**

Technological feasibility. **If it**  **is determined**  **a technology**  **has not**  **been**

**incorporated into**  **residential products**  **or in**  **working prototypes,**  **then the**  **technology will** 

**not be**  **considered further.** 

**4­1**Practicability to manufacture, install, and service. **If it**  **is determined**  **that mass** 

**production of**  **a technology**  **in residential**  **products and**  **reliable installation**  **and servicing** 

**of the**  **technology could**  **not be**  **achieved on**  **the scale**  **necessary to**  **serve the**  **relevant**

**market by**  **the effective**  **date of**  **the standard,**  **then that**  **technology will**  **not be**  **considered**

**further.**

Impacts on equipment utility to consumers. **If a**  **technology is**  **determined to** 

**have significant**  **adverse impact**  **on the**  **utility of**  **a product**  **to significant**  **subgroups of** 

**consumers, or**  **results in**  **the unavailability**  **of any**  **covered product**  **types with**  **performance**

**characteristics (including**  **reliability), features,**  **size, capacities,**  **and volumes**  **that are** 

**substantially the**  **same as**  **products generally**  **available in**  **the United**  **Sates at**  **the time,**  **it**

**will not**  **be considered**  **further.**

Safety of technologies. **If it**  **is determined**  **a technology**  **will have**  **significant**

**adverse impacts**  **on health**  **or safety,**  **it will**  **not be**  **considered further.** 

**In sum,**  **if DOE**  **determines that**  **a technology,**  **or a**  **combination of**  **technologies do** 

**not meet**  **the four**  **criteria above**  **it will**  **be eliminated**  **from consideration.**  **If a**  **particular**

**technology fails**  **to meet**  **one or**  **more of**  **the four**  **criteria, it**  **will be**  **screened out.**  **The**

**reasons for**  **eliminating any**  **technology are**  **documented in**  **section 4.2.** 

4.2 SCREENED­OUT TECHNOLOGIES

**This section**  **describes the**  **technologies that**  **DOE eliminated**  **for failure**  **to meet** 

**one of**  **the following**  **four factors:**  **1) technological**  **feasibility; 2)**  **practicability to** 

**manufacture, install,**  **and service;**  **3) impacts**  **on equipment**  **utility to**  **consumers; or**  **4)**

**consumer health**  **or safety.** 

4.2.1 Water Heaters

**DOE eliminated**  **the following**  **technology options**  **for residential**  **water heaters** 

**from further**  **consideration: side­arm**  **heater, flue**  **damper (buoyancy**  **operated), directly** 

**fired, condensing**  **pulse combustion,**  **advanced forms**  **of insulation,**  **thermophotovoltaic**

**and thermoelectric**  **generators, U­tube**  **flue, reduced**  **burner size**  **(slow recovery),**  **two**

**phase thermosiphon**  **(TPTS), and**  **CO 2**  **heat pump**  **water heater.** 

4.2.1.1 Side­Arm Heater (Gas and Oil Storage)

**Side­arm heaters**  **circulate the**  **potable water**  **between the**  **tank and**  **an external**  **heat**

**exchanger, typically**  **a shell­in­tube**  **exchanger. The**  **side­arm heater**  **design avoids**  **large**

**flue losses**  **by removing**  **the flue**  **from the**  **center of**  **the gas­ or**  **oil­fired storage**  **tank.**

**Side­arm storage**  **water heaters**  **are not**  **commercially available,**  **although products** 

**incorporating side­arm**  **heaters have**  **been commercially**  **available in**  **small quantities.** 

**However, DOE**  **was not**  **been able**  **to identify**  **a current**  **working prototype**  **for gas**  **or oil** 

**fired storage**  **water heaters,**  **and believes**  **manufacturers no**  **longer use**  **this technology.** 

**Therefore, it**  **is not**  **technologically feasible**  **and not**  **practical to**  **manufacture, install,**  **and**

**4­2 service**  **side­arm storage**  **water heaters**  **on the**  **scale necessary**  **to serve**  **the relevant**  **market**

**at the**  **time of**  **the effective**  **date of**  **the standard.** 

4.2.1.2 Flue Damper (Buoyancy Operated) (Gas Storage)

**This flue**  **damper is**  **a small,**  **very lightweight**  **aluminum dome­shaped**  **poppet that** 

**is lifted**  **by the**  **buoyancy of**  **the combustion**  **products to**  **allow flue**  **gases to**  **enter the** 

**venting system.**  **This technology**  **option would**  **reduce off­cycle**  **standby losses**  **by sealing** 

**the flue**  **and preventing**  **convection to**  **the venting**  **system, but**  **would have**  **no effect**  **on**

**recovery efficiency**  **because it**  **does not**  **affect the**  **rate of**  **heat transfer.**  **This flue**  **damper**

**may not**  **work with**  **high­recovery efficiency**  **water heaters**  **because there**  **may not**  **be**

**enough waste**  **heat in**  **the combustion**  **products to**  **provide sufficient**  **buoyancy to**  **lift the** 

**poppet.**

**Safety concerns**  **exist because**  **the damper**  **may not**  **open due**  **to the**  **low energy**  **of**

**the combustion**  **products. If**  **the flue**  **is blocked,**  **safety interlocks**  **should prevent**  **the gas** 

**storage water**  **heater from**  **operating. Otherwise,**  **harmful combustion**  **products will**  **enter**

**the space**  **where the**  **water heater**  **is installed**  **(** i.e.

**, residence).**  **Although safety**  **interlocks**

**can mitigate**  **improper exhaustion,**  **the water**  **heater would**  **still be**  **inoperable. Therefore,** 

**DOE does**  **not consider**  **buoyancy operated**  **flue dampers**  **for gas­fired**  **storage water** 

**heaters a**  **means to**  **improve EF**  **due to**  **the adverse**  **impacts on**  **safety.**

4.2.1.3 Directly Fired (Gas and Oil Storage)

**A directly**  **fired gas­ or**  **oil­fired storage**  **water heater**  **uses a**  **direct contact**  **heat**

**exchange process**  **that puts**  **potable water**  **directly into**  **contact with**  **the burner**  **flame and** 

**flue products.**  **Spraying the**  **water directly**  **at the**  **flame is**  **a more**  **efficient means**  **of**

**transferring heat**  **than in**  **a conventional**  **shell­and­tube heat**  **exchanger because**  **the heat** 

**resistive barrier**  **between the**  **water and**  **the flue**  **products is**  **eliminated. However,**  **this can** 

**also lead**  **to contamination**  **of domestic**  **water by**  **the flue**  **products, which**  **can cause**  **health**

**and safety**  **problems for**  **end users.**  **This technology**  **can also**  **conflict with**  **local plumbing** 

**codes (**  e.g.

**, International**  **Association of**  **Professional Plumbing**  **and Mechanical**  **Officials**

**(IAPMO) 1991)**  **with respect**  **to water**  **quality. Therefore,**  **this technology**  **is screened**  **out**

**because of**  **the adverse**  **impacts on**  **health and**  **safety.**

4.2.1.4 Condensing Pulse Combustion (Gas, Oil Storage, and Instantaneous)

**Pulse combustion**  **burners operate**  **on self­sustaining**  **resonating pressure**  **waves**

**that alternately**  **rarefy the**  **combustion chamber.**  **Pulse combustion**  **systems are**  **capable of** 

**self­venting, and**  **can draw**  **outside air**  **for combustion**  **even when**  **installed inside.**  **Pulse**

**combustion technologies**  **can achieve**  **high steady­state**  **efficiencies and**  **condensing**

**operation without**  **the use**  **of fans**  **or blowers.** 

**Prototype gas­ and**  **oil­fired storage**  **and instantaneous**  **water heaters**  **incorporating**

**pulse combustion**  **technologies have**  **been developed**  **in the**  **past. However,**  **this**

**technology is**  **not prevalent**  **among commercially**  **available products,**  **or even**  **among**

**water heater**  **research efforts.**  **Although condensing**  **pulse combustion**  **technology shows** 

**promising results**  **in increasing**  **EF, it**  **has not**  **yet penetrated**  **the gas­fired**  **storage, oil­fired** 

**4­3 storage,**  **and instantaneous**  **water heater**  **markets. Therefore,**  **it is**  **not technologically** 

**feasible and**  **not practicable**  **to manufacture,**  **install, and**  **service condensing**  **pulse**

**combustion technology**  **on the**  **scale necessary**  **to serve**  **the relevant**  **market at**  **the time**  **of**

**the effective**  **date of**  **the standard.** 

4.2.1.5 Advanced Forms of Insulation (Gas, Electric, and Oil Storage)

**Insulating gas­fired,**  **electric, and**  **oil­fired storage**  **water heaters**  **with vacuum,** 

**inert gases,**  **aerogel, or**  **evacuated panels**  **is an**  **alternative to**  **increasing the**  **thickness of** 

**the insulation**  **to decrease**  **heat transfer**  **and standby**  **losses. Manufacturers**  **elect to**  **use**

**alternative types**  **of insulation**  **because increasing**  **the thickness**  **of insulation**  **may create** 

**shipping and**  **installation problems**  **if diameters**  **exceed standard**  **building clearance** 

**widths. However,**  **several factors**  **limit the**  **inclusion of**  **advanced forms**  **of insulation**  **into**

**products today.** 

**To the**  **best of**  **DOE’s knowledge,**  **vacuum insulation**  **technology has**  **not been** 

**demonstrated for**  **water heater**  **applications for**  **either production**  **or prototyping.** 

**Durability and**  **maintaining the**  **seal over**  **the life**  **of the**  **storage water**  **heater are**  **some**

**problems of**  **vacuum insulation.**  **Although vacuum**  **insulation shows**  **promising potential** 

**for increasing**  **EF, no**  **manufacturer has**  **incorporated this**  **technology into**  **a commercially** 

**available product.**  **Thus, the**  **reliability over**  **the life**  **of the**  **water heater**  **has not**  **been**

**demonstrated. Therefore,**  **it is**  **not technologically**  **feasible and**  **not practicable**  **to**

**manufacture, install,**  **and service**  **vacuum insulation**  **technology for**  **gas­fired, electric,**  **and**

**oil­fired storage**  **water heaters**  **on the**  **scale necessary**  **to serve**  **the relevant**  **market at**  **the**

**time of**  **the effective**  **date of**  **the standard.** 

**Gas­filled panel**  **technology has**  **not been**  **demonstrated for**  **water heater** 

**applications for**  **both production**  **and prototyping,**  **to the**  **best of**  **DOE’s knowledge.**  **1**

**Prototypes have**  **been developed**  **for other**  **applications and**  **insulation improvements**  **have**

**been achieved.**  **However, gas­filled**  **panel technology**  **has not**  **yet penetrated**  **the gas­fired,** 

**electric, and**  **oil­fired storage**  **water heater**  **markets. Therefore,**  **it is**  **not technologically** 

**feasible and**  **not practicable**  **to manufacture,**  **install, and**  **service gas­filled**  **panel**

**technology for**  **gas­fired, electric,**  **and oil­fired**  **storage water**  **heaters on**  **the scale** 

**necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date of**  **the standard.** 

**Aerogel insulation**  **technology has**  **not been**  **demonstrated in**  **any commercially** 

**available water**  **heater applications**  **to the**  **best of**  **DOE’s knowledge.**  **Although aerogel** 

**insulation shows**  **promising potential**  **for increasing**  **EF, it**  **has not**  **yet penetrated**  **the**

**storage water**  **heater market**  **because manufacturers**  **must first**  **address potential**  **problems.**

**Aerogel insulation**  **is vulnerable**  **to shock**  **and vibration,**  **which may**  **create shipping**  **and**

**installation problems**  **if specific**  **handling techniques**  **are required.**  **In addition,**  **it is** 

**hygroscopic and**  **requires thorough**  **sealing within**  **the cavity**  **to prevent**  **exposure to**  **water**

**sources. Therefore,**  **it is**  **not technologically**  **feasible and**  **not practicable**  **to manufacture,** 

**install, and**  **service aerogel**  **insulation technology**  **for gas­fired,**  **electric, and**  **oil­fired**

**storage water**  **heaters on**  **the scale**  **necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the**

**effective date**  **of the**  **standard.**

**4­4 Evacuated­panel**  **technology has**  **not been**  **demonstrated for**  **water heater** 

**applications for**  **both production**  **and prototyping,**  **to the**  **best of**  **DOE’s knowledge.** 

**Prototypes have**  **been developed**  **for other**  **applications and**  **insulation improvements**  **have**

**been achieved.**  **However, evacuated­panel**  **technology has**  **not yet**  **penetrated the**  **gas**

**fired, electric,**  **and oil­fired**  **storage water**  **heater markets.**  **Therefore, it**  **is not** 

**technologically feasible**  **and not**  **practicable to**  **manufacture, install,**  **and service** 

**evacuated­panel technology**  **for gas­fired,**  **electric, and**  **oil­fired storage**  **water heaters**  **on**

**the scale**  **necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date of**  **the**

**standard.**

4.2.1.6 Thermophotovoltaic and Thermoelectric Generators (Gas, Oil Storage, and

Instantaneous)

**Both thermophotovoltaic**  **and thermoelectric**  **generators convert**  **a portion**  **of the** 

**energy produced**  **by a**  **gas­ or oil­fired**  **water heater**  **burner into**  **electricity to**  **supply**

**auxiliary components.**  **This avoids**  **the requirement**  **of a**  **conventional auxiliary**  **power**

**supply. Industry**  **has conducted**  **research on**  **developing thermophotovoltaic**  **and**

**thermoelectric technologies**  **to supply**  **electricity to**  **water heaters.**  **For example,** 

**thermoelectric generators**  **are used**  **for pilot**  **light safety**  **valves. However,**  **this technology** 

**option has**  **not been**  **developed to**  **supply auxiliary**  **power for**  **larger applications,**  **such as** 

**fans or**  **electromechanical dampers,**  **for use**  **with water**  **heater products.**  **Currently, it**  **is not** 

**practical to**  **manufacture, install,**  **or service**  **thermophotovoltaic and**  **thermoelectric**

**generator technology**  **for water**  **heaters on**  **a scale**  **necessary to**  **serve the**  **relevant market.** 

**Therefore, these**  **technology options**  **are not**  **considered technologically**  **feasible.**

4.2.1.7 U­Tube Flue (Gas and Oil Storage)

**The standard**  **length of**  **a flue**  **in a**  **gas or**  **oil­fired water**  **heater is**  **doubled by** 

**incorporating an**  **inverted U­shaped**  **flue into**  **the water**  **heater. A**  **U­tube flue**  **increases the** 

**heat transfer**  **by increasing**  **the heat**  **transfer surface**  **area. Additionally,**  **a U­tube**  **reduces**

**standby losses**  **because the**  **shape resists**  **heat convection,**  **similar to**  **a flue**  **damper.**

**U­tube flue**  **technology is**  **not incorporated**  **into any**  **commercially available**  **gas or** 

**oil­fired water**  **heaters. Prototypes**  **have been**  **developed and**  **research is**  **currently**

**underway. However,**  **this technology**  **has not**  **been successfully**  **demonstrated in**  **the**

**market, and**  **the energy**  **efficiency benefits**  **can not**  **be determined**  **due to**  **the lack**  **of**

**available products.**  **Therefore, it**  **is not**  **practical to**  **manufacture U­tube**  **flue technology**  **to**

**serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date of**  **this standard.** 

4.2.1.8 Reduced Burner Size (Slow Recovery) (Gas, Oil Storage, and Instantaneous)

**Decreasing the**  **burner size**  **to increase**  **the ratio**  **of heat**  **transfer area**  **to energy** 

**input can**  **increase the**  **recovery efficiency**  **of gas**  **and oil­fired**  **and instantaneous**  **water**

**heaters. However,**  **the decreased**  **input decreases**  **the recovery**  **rate, which**  **in turn,**  **would**

**most likely**  **reduce the**  **first­hour rating.**  **(First­hour rating**  **directly relates**  **to the**  **amount of** 

**hot water**  **the water**  **heater can**  **supply to**  **the consumer.)**  **This derating**  **of the**  **water heater** 

**adversely affects**  **the utility**  **to consumers.**  **Additionally, first­hour**  **rating is**  **directly**

**4­5 related**  **to burner**  **size: as**  **burner size**  **decreases, the**  **amount of**  **hot water**  **available to**  **the**

**consumer also**  **decreases. Therefore,**  **DOE will**  **not consider**  **this technology**  **option.**

4.2.1.9 Two­Phase Thermosiphon (Gas and Oil Storage)

**A two­phase**  **thermosiphon (TPTS)**  **removes the**  **flue from**  **the center**  **of a**  **gas or** 

**oil­fired storage**  **water heater**  **and places**  **a heat**  **exchanger outside**  **of the**  **storage tank** 

**reducing standby**  **losses. This**  **is similar**  **to the**  **side­arm heater**  **technology option.** 

**Manufacturers have**  **developed working**  **prototype water**  **heaters using**  **TPTS.**

**Several units**  **are commercially**  **available for**  **solar water**  **heating applications,**  **but not**  **for**

**gas or**  **oil­fired storage**  **water heating.**  **TPTSs used**  **for solar**  **applications rely**  **on large** 

**designs with**  **large surface**  **areas to**  **maximize sun**  **exposure. Large**  **TPTSs are**  **not practical** 

**for indoor**  **installations using**  **gas or**  **oil. Also,**  **incorporating the**  **TPTS system**  **would**

**cause a**  **drastic redesign**  **of all**  **gas and**  **oil­fired storage**  **water heaters**  **with little**  **increase in** 

**energy efficiency.**  **The redesign**  **would involve**  **removing the**  **center flue**  **and relocating**  **it**

**outside the**  **tank. As**  **a result,**  **only the**  **standby losses**  **would decrease**  **with no**  **affect on** 

**steady­state efficiency.** 

**TPTS for**  **gas and**  **oil­fired water**  **heaters is**  **currently being**  **researched. Therefore,** 

**it is**  **not practicable**  **to manufacture,**  **install, and**  **service this**  **technology on**  **the scale** 

**necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date of**  **the standard.** 

4.2.1.10 CO 2 Heat Pump Water Heater (Electric Storage)

**CO 2**  **heat pump**  **water heaters**  **use carbon**  **dioxide as**  **a natural**  **refrigerant to** 

**transfer heat**  **from the**  **surrounding air**  **to the**  **water stored**  **in the**  **tank through**  **a heat**  **pump**

**loop. Current**  **products and**  **prototypes can**  **achieve coefficients**  **of performance**  **as high**  **as**

**3.0, 2**  **which correspond**  **to EFs**  **ranging from**  **approximately 1.0**  **to 3.0.**  **This range** 

**accounts for**  **differences in**  **ambient air**  **conditions, storage**  **tank efficiency,**  **and**

**efficiencies of**  **the components**  **that make**  **up the**  **heat pump**  **loop. Additionally,**  **products**

**are capable**  **of functioning**  **in cold**  **weather climates**  **without freezing**  **pipes or**  **frosting**

**evaporators on**  **outdoor installations.**  **Products are**  **predominantly available**  **outside of** 

**U.S. markets**  **where they**  **have been**  **made available**  **by government**  **subsidy rebate** 

**programs. 3**  **The necessary**  **infrastructure to**  **support manufacturing,**  **installation, and** 

**service of**  **a CO**  **2 heat**  **pump water**  **heater is**  **not available**  **in the**  **United States**  **on the**  **scale**

**necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date of**  **the standard.** 

**Therefore, DOE**  **no longer**  **considers CO**  **2 heat**  **pump water**  **heaters for**  **the engineering** 

**analysis.**

4.2.2 Direct Heating Equipment

**The following**  **technology options**  **are screened**  **out for**  **residential direct**  **heating**

**equipment: increased**  **heat transfer**  **coefficient, power**  **burner, condensing**  **pulse**

**combustion, and**  **improved fan**  **or blower**  **motor efficiency.** 

**4­6**4.2.2.1 Increased Heat Transfer Coefficient (Fan Wall, Gravity Wall, Floor, Room,

Hearth)

**An alternative**  **to increasing**  **the size**  **of the**  **heat exchanger**  **is enhancing**  **the inside** 

**and outside**  **heat transfer**  **coefficients of**  **the heat**  **exchanger. Incorporating**  **dimples or** 

**some other**  **surface feature**  **to enhance**  **turbulence can**  **increase the**  **heat transfer**  **coefficient**

**when correctly**  **designed. Also,**  **the heat**  **exchanger may**  **be constructed**  **of a**  **material with** 

**a higher**  **thermal conductivity**  **than the**  **standard cold**  **rolled steel**  **that is**  **typically used.** 

**Increasing the**  **heat transfer**  **coefficient for**  **direct heating**  **equipment is**  **still in**  **the**

**research stages**  **and prototypes**  **have been**  **developed. However,**  **this technology**  **has not** 

**been demonstrated**  **in the**  **relevant market,**  **and the**  **energy efficiency**  **benefits cannot**  **be**

**determined due**  **to a**  **lack of**  **available products.**  **Currently, it**  **would not**  **be practical**  **to**

**manufacture this**  **technology to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date**

**of this**  **standard. DOE**  **does not**  **consider increased**  **heat transfer**  **coefficient any**  **further as** 

**a technology**  **for direct**  **heating equipment.** 

4.2.2.2 Power Burner (Fan Wall, Gravity Wall, Floor, Room, Hearth)

**Fan­assisted combustion**  **can be**  **accomplished by**  **power burner**  **systems**

**positioned upstream**  **of the**  **combustion zone.**  **Power burners**  **use blowers**  **upstream of**  **the**

**combustion zone**  **to supply**  **a more**  **efficient fuel­air**  **mixture to**  **the burner.**  **Power burners** 

**also reduce**  **off­cycle losses**  **by restricting**  **air flow**  **and convection**  **of warm**  **air to**  **the vent** 

**system, similar**  **to a**  **vent or**  **combustion box**  **damper.**

**Power burners**  **are typically**  **associated with**  **larger scale**  **applications including** 

**commercial furnaces,**  **boilers, and**  **oil­fired water**  **heaters. Additionally,**  **power burners**  **are**

**typically used**  **for high**  **input devices**  **that operate**  **over 100,000**  **Btu/h, although**  **units**

**operating below**  **this level**  **do exist.**  **The direct**  **heating equipment**  **identified in**  **this**

**rulemaking operates**  **below this**  **rating, on**  **average. The**  **product classes**  **identified for**  **this**

**rule range**  **from 10,000**  **Btu/h and**  **less to**  **46,000 Btu/h**  **and higher,**  **and the**  **majority of** 

**products fall**  **between these**  **ranges. The**  **average product**  **has an**  **input rating**  **of**

**approximately 39,000**  **Btu/h. Space**  **near the**  **combustion chamber**  **must be**  **allocated for** 

**the power**  **burner as**  **well. DOE**  **surveyed manufacturing**  **literature, which**  **suggests that** 

**approximately 1**  **cubic foot**  **of space**  **is required**  **for power**  **burners with**  **inputs from** 

**30,000 to**  **200,000 Btu/h.**  **Assuming no**  **space is**  **available for**  **a power**  **burner, 1**  **cubic foot** 

**would be**  **approximately more**  **than a**  **10­percent increase**  **in volume**  **for the**  **average heater** 

**covered by**  **this rule.** 

**Power burners**  **are still**  **being researched,**  **and development**  **for small**  **applications**

**such as**  **gas­fired direct**  **heating equipment**  **is still**  **underway. It**  **is not**  **practical to** 

**manufacture this**  **technology to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date**

**of this**  **standard. DOE**  **will not**  **consider power**  **burners any**  **further in**  **the engineering** 

**analysis.**

**4­7**4.2.2.3 Condensing Pulse Combustion (Fan Wall, Gravity Wall, Floor, Room,

Hearth)

**Pulse combustion**  **burners operate**  **on self­sustaining**  **resonating pressure**  **waves**

**that alternately**  **rarefy the**  **combustion chamber.**  **Pulse combustion**  **systems are**  **capable of** 

**self­venting, and**  **can draw**  **outside air**  **for combustion**  **even when**  **installed inside.**  **Pulse**

**combustion technologies**  **can achieve**  **high steady­state**  **efficiencies and**  **condensing**

**operation without**  **fans or**  **blowers.**

**Similar to**  **the condensing**  **pulse combustion**  **technology option**  **considered for** 

**residential water**  **heaters, this**  **pulse combustion**  **technology is**  **not prevalent**  **among**

**commercially available**  **DHE products.**  **Therefore, the**  **pulse combustion**  **technology**

**option will**  **not be**  **considered as**  **a means**  **to condense**  **flue gases**  **in direct**  **heating**

**equipment because**  **it is**  **not technologically**  **feasible for**  **DHE applications.** 

4.2.2.4 Improve Fan or Blower Motor Efficiency (Fan Wall, Hearth)

**Fan or**  **blower motor**  **efficiency can**  **be increased**  **to reduce**  **the electrical**  **energy**

**consumption of**  **the DHE**  **by using**  **a brushless**  **direct current**  **(DC) motor,**  **which**

**eliminates the**  **friction caused**  **by the**  **brushes of**  **a permanent**  **split capacitor**  **(PSC) motor.** 

**Assuming a**  **fan or**  **blower motor**  **installed in**  **DHE is**  **a 1/20**  **horsepower motor** 

**(approximately 127**  **Btu/h) and**  **is operating**  **as low**  **as 50­percent**  **efficiency, the**  **resulting**

**energy consumption**  **of the**  **motor is**  **small. Assuming**  **a heater**  **operates at**  **an input**  **of**

**approximately 45,000**  **Btu/h or**  **greater, the**  **motor accounts**  **for less**  **than one**  **percent of** 

**the total**  **power consumption**  **of the**  **direct heating**  **equipment. Motor**  **efficiency could** 

**improve by**  **approximately 20**  **percent when**  **switching from**  **PSC to**  **brushless motors;** 

**however, the**  **overall improvement**  **to the**  **DHE is**  **less than**  **one percent.** 

**Manufacturers of**  **DHE use**  **high­efficiency PSC**  **motors due**  **to their**  **modest cost,** 

**high efficiency,**  **compact design,**  **and durability.**  **Achieving more**  **efficient PSC**  **motor**

**designs for**  **DHE applications**  **is an**  **ongoing challenge**  **and no**  **substantial gain**  **in energy** 

**efficiency has**  **occurred in**  **recent years.**  **Efficiency could**  **be improved**  **by increasing**  **rotor**

**surface area,**  **which would**  **increase overall**  **motor size.**  **However, energy**  **efficiency**

**improvements are**  **difficult to**  **achieve because**  **of size**  **constraints within**  **DHE and** 

**because the**  **affect on**  **energy efficiency**  **would be**  **low. Brushless**  **DC motors**  **may increase** 

**energy efficiency,**  **but this**  **technology has**  **not yet**  **penetrated the**  **market due**  **to cost** 

**constraints. Therefore,**  **it is**  **not practical**  **to manufacture,**  **install, and**  **service this** 

**technology for**  **fan wall**  **DHE on**  **the scale**  **necessary to**  **serve the**  **relevant market**  **at the** 

**time of**  **the effective**  **date of**  **the standard.** 

4.2.3 Pool Heaters

**The following**  **technology option**  **is screened**  **out for**  **pool heaters:**  **condensing**

**pulse combustion.** 

**4­8**4.2.3.1 Condensing Pulse Combustion

**Pulse combustion**  **burners operate**  **on self­sustaining**  **resonating pressure**  **waves**

**that alternately**  **rarefy the**  **combustion chamber**  **and draw**  **outside air**  **without fans**  **or**

**blowers. Additionally,**  **pulse combustion**  **technologies can**  **achieve high**  **steady­state**

**efficiencies and**  **condensing operation**  **without fans**  **or blowers.**  **High­efficiency gas­fired** 

**boilers using**  **pulse combustion**  **are currently**  **available. However,**  **pulse combustion**  **pool**

**heaters are**  **not known**  **to exist,**  **and DOE**  **did not**  **identify any**  **prototypes or**  **research**

**efforts. Therefore,**  **DOE is**  **not considering**  **this technology**  **option further**  **because it**  **is not** 

**technologically feasible**  **at this**  **time, and**  **it is**  **not practical**  **to manufacture,**  **install, and** 

**service on**  **the scale**  **necessary to**  **serve the**  **relevant market**  **at the**  **time of**  **the effective**  **date**

**of this**  **standard.**

4.3 REMAINING TECHNOLOGIES

**After eliminating**  **those technologies**  **that have**  **no effect**  **or do**  **not increase**  **energy**

**efficiency and**  **screening out**  **those technologies**  **that that**  **do not**  **meet the**  **requirements**

**prescribed at**  **10 CFR**  **part 430,**  **subpart C,**  **appendix A,**  **4(a)(4) and**  **5(b), DOE**  **is**

**considering the**  **technologies in**  **the following**  **list.**

• **Water Heaters** 

• **Insulation improvements** 

• **Increased jacket**  **insulation (gas,**  **electric, oil**  **storage)**

• **Insulated tank**  **bottom (electric**  **storage)**

• **Plastic tank**  **(electric storage)** 

• **Foam insulation**  **(gas, electric,**  **oil storage)** 

• **Heat Exchanger**  **Improvements**

• **Increased heat**  **exchanger surface**  **area (gas,**  **electric, oil**  **storage,**

**instantaneous)**

• **Enhanced flue**  **baffle (gas,**  **oil storage)** 

• **Submerged combustion**  **(gas, oil**  **storage)**

• **Multiple flues**  **(gas, oil**  **storage)**

• **Direct vent**  **(instantaneous)**

• **Alternative flue**  **geometry (helical)**  **(gas, oil**  **storage)**

• **Heat traps**  **(oil storage)** 

• **Power vent**  **(gas, oil**  **storage, instantaneous)** 

• **Flue damper**  **(electromechanical) (gas,**  **oil storage)** 

• **Electronic (or**  **interrupted) ignition**  **(gas, oil**  **storage, instantaneous)** 

• **Integral heat**  **pump water**  **heater (electric**  **storage)**

• **Condensing (gas,**  **oil storage,**  **instantaneous)**

**4­9**• **Direct Heating**  **Equipment**

• **Heat exchanger**  **improvements**

• **Increased heat**  **exchanger surface**  **area (fan**  **wall, gravity**  **wall, floor,** 

**room, hearth)** 

• **Multiple flues**  **(fan wall,**  **gravity wall,**  **floor, room,**  **hearth)**

• **Multiple turns**  **in flue**  **(fan wall,**  **gravity wall,**  **floor, room,**  **hearth)**

• **Direct vent**  **(concentric venting)**  **(fan wall,**  **gravity wall,**  **floor, room,** 

**hearth)**

• **Electronic ignition**  **(fan wall,**  **gravity wall,**  **floor, room,**  **hearth)**

• **Thermal vent**  **damper (fan**  **wall, gravity**  **wall, floor,**  **room, hearth)** 

• **Electrical vent**  **damper (fan**  **wall, gravity**  **wall, floor,**  **room, hearth)** 

• **Induced draft**  **(fan wall,**  **gravity wall,**  **floor, room,**  **hearth)**

• **Increased insulation**  **(floor)**

• **Condensing (fan**  **wall, gravity**  **wall, floor,**  **room, hearth)** 

• **Two­stage and**  **modulating operation**  **(fan wall,**  **gravity wall,**  **floor, room,** 

**hearth)**

• **Air circulation**  **fans (floor,**  **room, hearth)** 

• **Sealed combustion**  **(fan wall,**  **gravity wall,**  **floor, room,**  **hearth)**

• **Pool Heaters** 

• **Electronic Ignition** 

• **Improved heat**  **exchanger design** 

• **More effective**  **insulation (combustion**  **chamber)**

• **Power venting** 

• **Sealed combustion** 

• **Condensing**

**4­ 10** REFERENCE

**1 Lawrence**  **Berkeley National**  **Laboratory.** Gas Filled Panels

**. Last**  **accessed March** 

**19, 2008.**  **< http://gfp.lbl.gov/applications/default.htm>.** 

**2 Enhanced,**  **Compact and**  **Ultra­Compact Heat**  **Exchangers: Science,**  **Engineering**

**and Technology.**  Development of a New Type Heat Exchanger for Natural Refrigerant

CO 2 Heat Pump Water Heaters. **Last accessed**  **April 17,**  **2009.**

**< http://www.r744.com/knowledge/papers/files/pdf/pdf_190.pdf**  **>.**

**3 The**  **Latest Developments**  **in the**  **Use of**  **CO 2**  **as Refrigerant.**  IEA Heat Pump News

Letter

**. Volume**  **24, No.**  **3/2006. Last**  **accessed April**  **17, 2009.** 

**< http://www.heatpumpcentre.org/publ/HPCOrder/ViewDocument.aspx?RapportId=396**  **>**

**.**

**4­ 11**