Construction and Energy Costs for Radiant System in ......• Demand controlled ventilation in large...

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Symposium: Optimizing Radiant Systems

Oct 23, 2019

Construction and Energy Costs for Radiant System in California Bay Area

© TRC Companies, Inc. All rights reserved

Acknowledgements• This work was done when the presenter worked at Taylor Engineering with

support from Hwakong Cheng and Steve Taylor

• This study was funded by California Energy Commission Electric Program Investment Charge (EPIC) under the Optimizing Radiant Systems for Energy Efficiency and Comfort project, led by Center for the Built Environment at UC Berkeley


• Project overview

• Case study building

• Cost data

• How to reduce construction costs

• Energy performance

• How to reduce energy costs

Agenda


Objectives§ Provide cost data for radiant systems in California Bay Area§ Suggest opportunities to reduce cost and improve energy

efficiency

Approach§ Provide baseline and alternative design options § Cost estimation by contractors§ Energy performance evaluation by EnergyPlus

Project Overview


BackgroundStatus of VAV § Predominant HVAC approach

• Optimized construction process• Competitive market

§ Design guidelines• Advanced VAV System Design Guide• ASHRAE Guideline 36

Status of radiant § Small market share, mostly in low-energy and ZNE projects

§ Limited design guidelines and tools

§ Lack of familiarity by building construction industry

Image: an online map of radiant system buildings


Real building with radiant designSimplified floor plan§ Open office with meeting rooms§ Total floor area 112,000 ft2

Building features§ Solar load control

• Window-wall ratio 40%• Glazing U-value 0.4 and SHGC 0.28• Exterior overhang

§ LED lights and daylight control§ Advanced plug load control

Case study building

Image: EnergyPlus model of the case building


Radiant slab design

• High thermal mass radiant system with tubes in every ceiling slab

• 10 radiant zones per typical floor

• 13 DOAS VAV zones per typical floor

• Demand controlled ventilation in large conference rooms

Radiant slab zoning plan (part of typical floor) DOAS zoning plan (part of typical floor)


Radiant system designDedicated outdoor air system (DOAS)§ Design air flowrate

19,400 cfm§ Changeover

heating/cooling coil

Central plant § Four-pipe air source

heat pump § Serves both DOAS and

radiant slabs to reduce cost

Radiant design schematic


Construction costsHVAC and controls only

Common mechanical elements NOT included

San Mateo labor rate• Sheet metal: $123/hr• Piping: $118/hr

Results§ Average : $38.9/ft2


Construction cost breakdown

44% of total cost

20% of total cost


Piping labor breakdown

Radiant slab: $6.6/ ft2

Floor distribution + risers: $2.9/ ft2

Radiant slab ($6.59 / 46%)

Terminals ($1.25 / 9%)

Floor Distribution ($1.91 / 13%)

Roof Equipment ($1.19 / 8%)

Risers ($0.98 / 7%)

Miscellaneous ($2.27 / 16%)


Equipment Cost

Radiant equipment: $2.82/ ft2

DOAS AHU : $0.79/ ft2

ASHP: $2.71/ ft2

AHU ($0.79 /11.5%)

ASHP ($2.71 /39.0%)

Radiant tubes/mats ($2.82 /40.7%)

VAV/Dampers ($0.21 /3.1%)

Hydronic ($0.25 /3.6%)

Grilles ($0.14 /2.1%)


Impact of labor rate

• National average labor rate: $85/hr

How to reduce radiant system cost?


Facilitate the use of radiant mat

Costs§ Mats : ~$4 - 6 /ft2

§ Loops*: ~$6 - 8 /ft2

Limitations for mats§ Maybe limited by shape and size

of radiant zones§ May not be cost effective for

smaller jobs (assembled on a made-to-order basis)

* For 6-inch tube spacing

Radiant roll-out mat

Traditional loops


Hydronic distribution layout: Multiple risers vs. single riser

§ Strategically locate risers to minimize piping: 30% piping reduction§ Cost savings: $2.5/ft2

Multiple risers: Typical floor piping layoutSingle riser: Typical floor piping layout

Single HW/CHW riser


Use larger radiant tube spacing: 9” vs. 6 in”

§ Loop design: ~$1.7/ft2 of labor cost savings § Mat design : 5-15% cost savings and 5% labor savings§ Thermal capacity: initial evaluation shows similar dynamic

performance


Other approaches to reduce radiant costs

§ Large vs. small radiant zones§ Consider no radiant tubes in ground or roof slab § Use passive supplemental system strategically (For example, ceiling

fans)§ Hydronic system type: 4-pipe vs. 2-pipe vs. mixed 4 and 2-pipes § Reduce central plant equipment size with load shifting § More details in the report*

*Feng, J., & Cheng, H. (2018). Comparison of Construction and Energy Costs for Radiant vs. VAV Systems in the California Bay Area. Deliverable for California Energy Commission Project EPIC -14-009, Taylor Engineering. Retrieved from https://escholarship.org/uc/item/13h9z4gg


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HVAC annual site electricity

Total: 2.9 kBtu/ft2

§ Cooling is 41% of total energy§ Fan energy is 34% of total energy


Central plant cooling and heating load• Cooling energy use in winter months• DOAS uses significant energy

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Radiant Slab _heat DOAS_heat Radiant Slab _cool DOAS_cool Monthly Ave OADB

How to reduce radiant system energy cost?


Potential for economizer to reduce cooling energy

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Potential full airside economizer hours


Implement load shifting strategy to reduce demand

Radiant slab operates 6 am - 6 pm

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Radiant_DOAS Radiant_Slab OADB

Radiant slab operates 0 am-12 pm


Implement load shifting strategy to reduce demand

- Whole building electricity cost- High performance design to minimize heat gain is key

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Radiant run at different operation periods


Optimize DOAS supply air temperature control

Neutral SAT

Large deadband

OA reset


Optimize DOAS supply air temperature control§ Use large heating/cooling setpoint deadband§ Reset supply air temperature higher with space humidity

feedback

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HeatPumpCooling HeatPumpHeating Pump Fan

Traditional controlReset with large deadband


Approaches to reduce energy cost§ Take advantage of free cooling with waterside economizer ( mild

weather in particular )§ Implement load shifting strategy to reduce demand charge and

equipment size§ DOAS design and control are critical

o DOAS supply air temperature control is IMPORTANTo Avoid unnecessary oversizing of DOAS by strategically distributing

the ventilation air o Decouple cooling source for radiant slab and DOAS in humid

climates§ More details in the report*

There are opportunities for improving current practice!

*Feng, J., & Cheng, H. (2018). Comparison of Construction and Energy Costs for Radiant vs. VAV Systems in the California Bay Area. Deliverable for California Energy Commission Project EPIC -14-009, Taylor Engineering. Retrieved from https://escholarship.org/uc/item/13h9z4gg

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