[Equest-users] ERV equivalent in baseline model?

[Nathan Miller]

Is this a project using the LEED for Homes Midrise protocol with the ENERGY STAR Multifamily High Rise Simulation Guidelines? If so, it is worth noting that while you are (probably) grand fathered in with whichever version of the ESMFHR Sim Guidelines that were in place when the project registered for LEED, you also have the option of using the more updated versions.

We've found that the latest release (dated Sept 2013) contains significantly more detail on how to select the baseline system than the previous versions. I don't entirely agree with the rationale in this document (I think there is some twisting of the 90.1 language), but at least it tries to sort things out. I *think* you would fall under the example 3 in the below excerpt?

Link: http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/mfhr/ENERGY_STAR_MFHR_Simulation_Guidelines_Version_1.0_Rev02.pdf

Some Key Excerpts:
3.8 HVAC
3.8.1 Every space that is modeled as cooled in the Proposed Design simulation shall  also be modeled as cooled in the Baseline Building Design. Likewise, every space that is modeled as heated in the Proposed Design simulation shall also be modeled as heated in the Baseline Building Design. Unconditioned and semi-heated spaces shall also match between the Proposed Design simulation and Baseline Building Design.

a. Model the entire living (including all dwelling unit) space, as well as offices, community rooms and other conditioned spaces, except as described below, as heated and cooled.

b. Do not model cooling in corridors and utility spaces such as mechanical rooms, laundry rooms, etc. unless the spaces are cooled in the Proposed Design. Per addendum dn to ASHRAE 90.1-2007, such thermal zones shall be modeled using constant volume Heating and Ventilation systems in the Baseline Building Design. The heating source shall be warm-air furnace, gas-fired, if the building's predominant heating source is Fossil Fuel, Fossil/Electric Hybrid, or Purchased Heat, and warm-air furnace, electric resistance in other cases. System design supply airflow rates for these baseline systems shall be based on the temperature difference between a supply air temperature setpoint of 105°F and the design space heating temperature setpoint; the minimum outdoor air flow rate; or the air flow rate required to comply with applicable codes or accreditation standards, whichever is greater. Each thermal block shall be modeled with a separate HVAC system and the following baseline fan power:

Pfan,supply = CFMs * 0.3.
Pfan,supply        electric power to supply fan motor (watts)
CFMs      the baseline system maximum design supply fan airflow rate  in cfm

3.8.2 The Baseline and Proposed HVAC system shall be modeled as per Appendix G, and as clarified in the first note below Appendix G Table G3.1.1A, "...Residential building types include dormitory, hotel, motel, and multifamily." Following this note, common spaces that are essential to the building's residential function, including but not limited to corridors and stairwells, must be modeled with residential baseline HVAC system type (System 1 or 2 only) depending on the predominant fuel source in the building, except as allowed in 3.8.1. Appendix G exception G3.1.1(a) that allows the use of additional system types for nonpredominant conditions if they total more than 20,000 ft2, only applies to heating source, not space function. Baseline HVAC System Types 3-8 may not be used, except in appropriate nonresidential spaces that exceed 20,000 ft2.

Example 1: 25 story multifamily building heated predominantly with gas has 1,000 ft2 of common space on each floor, including corridors, trash rooms, and stairwells. Together, these spaces account for 25,000 ft2. Corridors are heated with gas and cooled. Stairs are heated with electric resistance but not cooled. What baseline system type should be modeled for the common spaces?
Correct Approach: Apartments and corridors are modeled with Baseline HVAC System 1-PTAC. Stairs that are heated but not cooled are modeled with Heating and Ventilation System as described in 3.8.1, which results in Baseline HVAC System 11, not 10.
Incorrect Approach: Common spaces are modeled with baseline System 7 following exception G3.1.1(a), since they account for over 20,000 ft2 and cover more than 5
floors.

Example 2: 25 story multifamily building heated predominantly with electricity has 1,000 ft2 of common space on each floor, including corridors, trash rooms, and stairwells. Together, these spaces account for 25,000 ft2. Corridors are heated with gas and cooled, and account for 21,000 ft2. Stairs are heated with electric resistance but not cooled. What baseline system type should be modeled for the common spaces?
Correct Approach: Apartments are modeled with Baseline HVAC System 2-PTHP. Stairs that are heated but not cooled are modeled with Heating and Ventilation System
as described in 3.8.1, which results in Baseline HVAC System 10 since the building's predominant heating source is electric. Corridors can use Appendix G exception G3.1.1(a) in order to model Baseline HVAC System 1-PTAC in the corridors of the Baseline Building Design.

Example 3: 25 story multifamily building with electric heat pumps serving the apartments and corridors are heated with gas, but provide ventilation directly to the apartments. What baseline system type should be modeled for the apartments?
Correct Approach: This qualifies as fossil/electric hybrid and therefore apartments and corridors are modeled with Baseline HVAC System 1-PTAC.

Nathan Miller - PE, LEED®AP BD+C, CEM
Mechanical Engineer/Senior Energy Analyst
RUSHING | D 206-788-4577 | O 206-285-7100
www.rushingco.com<http://www.rushingco.com/>

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Tianyao Zhang
Sent: Friday, February 21, 2014 2:14 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] ERV equivalent in baseline model?

Hi all,

I'm modeling a LEED for Homes building, the proposed design uses Variable Refrigerant Flow systems with a rooftop Energy Recovery Unit providing 100% OA, everything is electric except the ERV unit, which uses natural gas. My baseline model system type is PTHP. My question is, since the proposed case has natural gas as one of its heating source, does the baseline case systems have to be revised to include natural gas as well? The problem is there isn't an ERV equivalent in the baseline model, so I'm not sure where to add the natural gas units, if necessary.

I appreciate any feedback on this matter, thank you!

--
Tianyao Zhang

M.S. Graduate in Architecture - High Performance Buildings
College of Architecture
Georgia Institute of Technology
Atlanta, GA
404-834-0120

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