Base case question

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Maybe someone can answer this for me:

?Using ASHRAE 90.1-1999 at the reference standard, what is the HVAC system
for the baseline building if the proposed building is a ground-source heat
pump with radiant heating and cooling? In Figure 11.4.3, the standard
indicates that System 6 should be used. System 6 is listed as a
water-source heat pump with direct expansion for cooling and electric heat
pump and boiler for heating. Is System 6 distributed water-source heat
pumps with a boiler for heat and a fluid cooler for cooling? Or is it a
ground-source heat pump with a boiler for peak demand and domestic hot


Chris Flood BSc (Eng)


Chris2's picture
Joined: 2011-10-02
Reputation: 400

Hi Chris,

Using Figure 11.4.3, the first step is to identify the principle heating
source (I would assume there are backup boilers for the ground-source heat
pumps in the proposed design). Per ASHRAE 90.1-1999 - 11.4.3.k.2, for
systems with mixed fuel heating sources, the principle heating source is the
one with the largest total installed output capacity. Hence, the Baseline
Case should be modeled as system 6 only if the total output capacity of the
geothermal heat pumps is larger than the total output capacity of the backup

In response to your second question, system 6 is distributed water-source
heat pumps with an atmospheric boiler (80% efficiency) and an axial fan
cooling tower with two-speed fans.


Ali Nazari, M.A.Sc.

Ali Nazari's picture
Joined: 2011-09-30
Reputation: 0