Residential Space and Water Heating: The Combined Approach - Schoenbauer

Residential Space and Water Heating: The Combined Approach

Ben Schoenbauer, Research Engineer, Center for Energy and Environment

May 22, 2012

How this project came about− Weatherization is able to seal homes tighter and tighter

− Leads to combustion safety issues

− Requires sealed combustion

− Requirements on savings vs. installed cost rule out high efficiency water heaters

− Forced to use safety budget to install 60% direct vent tanks with very little energy savings

− SRC replaces furnaces in 47% of the homes they weatherize and water heaters in 48%

− SRC got a Sustainable Energy Resources for Consumers (SERC) grant to look at using a DIA

Storage water heater based system

Storage Water Heater

DHW Loads

Cold In from Mains

Supply to AH

Return from AH

Hydronic Air

Handler

Hot Space Heating Air

Open Loop

Tankless water heater based system

DHW Loads

Cold In from Mains

Supply to AH

Return from AH

Hydronic Air

Handler


Electric Electric Gas

TWH

Combi boiler based systemDHW Loads

Cold In from Mains

Supply to AH

Return from AH

Hydronic Air

Handler


HE

DHW Loop

Space loop

Primary Loop Secondary Loop

Closed Loop

Combi Boiler

PROBLEM+ Some contractor’s had little experience

+ System schematics often developed on site

+ Little or no sizing information provided

+ System components came from several manufacturers

+ Manufacturer’s settings may not lead to best performance

+ Decided to design and optimize systems in a laboratory

+ Could then provide contractors with more detail installation guidelines

Installation and Sizing

+ Idle losses

+ Steady state efficiency

+ Air handler capacity testing

+ Full system tests

Lab work

Lab Testing

Idle Losses

Setpoint = 140 F$1/therm$0.12/kWh

Boiler 1 – Combi boiler with 12 gal DHW tank

Lab Tests – Idle Testing

TANK 2

Steady-State Space Heating Efficiency

Going from 90% to 80% increase heating bills about $150/year in MN

Tset=130F and Flow rate=4.0GPM

+ Minimum supply air temperature (110 F) for comfort dictates minimum flow rate

+ Maximum return water temperature (105 F) dictates maximum flow rate

+ Coil capacity is bounded by these flow rates

Air Handler Performance Mapping

At CFM=1100, Supply Water =140F, Return Air = 70F



52,500 – 57,000 kBtu/hr

45,500 – 54,000 kBtu/hr

+ 300 installs in Minnesota before December 2012+ Utility bill analysis on all 300 sites

+ Detailed pre/post monitoring on 20 sites

Field Implementation and Monitoring

Field Study: Expected Results

+ Better understanding of installed costs for different systems after contractors have become familiar

+ System design specifications and quality control requirements

+ Installed efficiencies of DIA systems and savings potential

Existing Equipment

DHW LoadsCold In from Mains


Runtime

Air Temp

Ambient T

Gas

ND Tank Water Heater

Electric Gas

Single Stage

Furnace

Conditioned Space

Outdoor

DIA Installation

DHW LoadsCold In from Mains

Supply to AH

Return from AH

Hydronic Air

Handler


Water TempWater Flow

Consumption

Air TempAir Flow

Electric

Ambient T

Electric Gas

Water Heater

Conditioned Space

Outdoor

EXISTINGCOMBI

Minneapolis Ave Outdoor Temp when Space Heating = 33 °FMinneapolis Design Outdoor Temp for Space Heating = 18 °F

Represents about a 250 therm/yr savings or about 25% of the gas heating (space + dhw) bill and 75% electricity use for space + dhw use

DHW about 1% of total output

Represents about a 120 therm/yr savings or about 20% of the gas heating (space + dhw) bill and 40% electricity use for space + dhw use

Very low hot water use only 5 gpd on ave.

PRELIMINARY: Comparison to a 93% AFUE Furnace

Represents about a 20 therm/yr increase or about 3% of the gas heating (space + dhw) bill and 20% electricity use reduction for space + dhw use

DHW about 1% of total output

700 kBtu/day ~ 28kbtu/hr space and 50 gpd at 70DT

250 kBtu/day ~ 10kbtu/hr space and 20 gpd at 70DT

0 20 40 60 80 100 120 140 160

Days with No Space Heating

Supply Air Temperature

Questions?

Ben Schoenbauer

[email protected]

Residential Space and Water Heating: The Combined Approach - Schoenbauer

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