Hello,
We have a situation where we are attempting to model a highrise building of approximately 450,000 square feet.
The predominant use of this building is residential. The proposed system will be a water source heat pump system. The residential portion of the building will be about 350,000 square feet. Therefore, we would foresee this being the predominant condition of this building.
The other 100,000 square feet will be split between office and retail. However, at the time the model is to be submitted, the office and retail will only be core and shell and the fitouts will be done in the future. The proposed system in the office and retail spaces would be a water source heat pump system as well.
I understand from CIR ID #10132 that the water source heat pump system is a ‘fossil fuel’ and we will choose the baseline systems accordingly.
The questions are as follows:
1. G3.1.1a states to use additional systems and fuel sources for nonpredominant conditions over 20,000 square feet. Does this mean that the single proposed building would need to be compared with a baseline building for the residence AND a baseline building for the retail/office? Is G3.1.1a an option or a requirement? Can we model the proposed building against a single baseline building that is PTAC with Fossil Fuel Boiler if we would wish to?
2. If the core commercial spaces are not defined prior to the model as ‘retail’ or ‘office’, do we select one schedule and loading per ASHRAE and make them identical conditions in the proposed and baseline?
3. If we must differentiate ‘office’ and ‘retail’ and each type is over 20,000 square feet, does that push us into 3 different baseline buildings? One for residential, one for retail and one for office?
Thanks in advance for any assistance you may be able to offer.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
May 8, 2012 - 8:27 pm
There are many potential variables in your questions. If your water source heat pump is all electric then use the electric column from Table G3.1.1. The CIR says if you have any fossil fuel in the system you need to use the fossil fuel column.
1. G3.1.1a is optional. The note in Table G3.1.1A says model the predominant condition.
2. Yes you can identify the use.
3. Only one baseline needed.
Wes Lawson
Mechanical EngineerBala Consulting Engineers
4 thumbs up
May 10, 2012 - 3:10 pm
Marcus,
Thank you very much. Your post addressed our first question as to whether G3.1.1a is a requirement or option. Since it is an option, we would proceed with a single baseline building rather than 2-3 baselines.
The second portion of our question would then pertain to how we would select the heating source in the baseline. Although the terminal heat pumps are electric, we would use purchased district steam to provide the heat required to maintain minimum temperatures of the loop. However, currently the corridor and residence ventilation rooftop unit would utilize natural gas for heating. The 100% outdoor air rooftop unit would also have an energy recovery wheel per the code requirements.
The questions for the heating source are as follows:
1. The steam would be the predominant heating source in the building due to the overall usage, as compared to the quantity of gas heat utilized by the rooftop unit. Would that push our baseline hot water heating system to be modeled with actual rates of the purchased heat per G3.1.1.1? Therefore, we would not be modeling any gas usage or boilers?
2. I read on a previous question on this site that the DOAS does not need to be modeled in the baseline. This would then require the baseline building to have the outdoor air modeled as being provided and conditioned through the individual baseline PTAC units. I would think that we would not need heat recovery on the baseline system since the ventilation is provided through the PTAC units and represents well less than 70% at any one unit. Also, it appears that the DOAS, and associated economizer, do not need to be modeled for climate zone 4A per G3.1.2.6 in the baseline. Is this correct?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
May 10, 2012 - 4:22 pm
1. If you have any fossil fuel heat then the baseline is fossil fuel. The User's Manual is more clear on the issue of purchased heat (page G23). The baseline includes the steam heat where used in the proposed and the gas where included in the proposed.
2. Sounds right to me.
Wes Lawson
Mechanical EngineerBala Consulting Engineers
4 thumbs up
May 29, 2012 - 1:29 pm
Marcus,
I would like to confirm one more item.
We currently have a steam service adding heat to the heat pump loop to maintain a minimum temperature. However, there is gas heat in the DOAS rooftop unit. This seems like it gets into a slight gray area when it comes to baseline heating services.
Our thought is that since the gas is for a DOAS system, which is not part of the baseline system, the baseline system should not reflect the rooftop unit service. Therefore, the steam would be the predominant heating source and our baseline building would be modeled with 'purchased heat'. Therefore, we are comparing our proposed building that largely uses steam for heating, with a steam baseline building. Do you agree? I would not think that the baseline would need to have a gas service at all.
Thanks again.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
May 30, 2012 - 8:51 am
Agreed. There would be no DOAS in the Baseline so no gas heat. After reviewing this thread it appears I was not correct about the gas heat in my May 10 post.
sasa weee
1 thumbs up
June 4, 2012 - 2:15 pm
Yeah you are totally correct about that.O and do visit and buy google plus one for better placement.