Hello,
I searched through existing posts and did not find a post regarding my question (though that doesn't mean that I searched very well) so please forgive me if this question has been asked and answered. If it has, please direct me to the thread.
We designed a a building in climate zone 4A, part of which is a two storey instruction facility. The downstairs portion of the facility consists of classroom spaces and support spaces (e.g. bathrooms). The upstairs spaces consists of some private offices, open floor offices, a conference room, and support spaces. The upstairs and downstairs each have a dedicated outside air system that provides dehumidified air (48-deg F dew point).
Both DOASes are partial recirculating type, have an enthalpy wheel, heating section, DX cooling coil, and hot gas reheat to temper the supply air. The downstairs DOAS supplies air to classroom chilled beams (the CB design has been reviewed by my peers as well as the chief engineer from Titus and it is considered sound) plus a couple of blower coils (where beams wouldn't be appropriate). The upstairs DOAS supplies dehumidified, room neutral air directly to the zones. The air volumes are based on providing ASHRAE 62.1 compliant ventilation airflow rates plus additional air to provide dehumidification of each space/zone (e.g. an office may only need 20-cfm of outside air, but may need 60-cfm of 48-degF dew point air to account for the latent load).
The facility will have an air barrier and non-operable windows. The space design conditions are 78-degF DB & 45%RH. A design infiltration rate of 0.1-cfm/sf of wall was used (based on ASHRAE Fundamentals for typical new construction) so the amount of air supplied to spaces for dehumidification takes into account any latent load from infiltration.
All that being said, the design did not include condensate piping for the upstairs' fan and blower coils based on the DOAS dehumidification. The building is under construction and the contractor has submitted an RFI regarding condensate piping (i.e. "it's not there, what do you want me to do?"). This is my first major design where I did not include the condensate piping based on having confidence in the design. But now that the question is being raised, I am having second thoughts. Our commissioning specialist doesn't have the warm and fuzzies and would feel better having the condensate pipe installed via a change order. I would certainly have the warm and fuzzies if we installed the condensate piping, but then what would have been the point of decoupling the latent and cooling loads with the DOAS (I ask rhetorically)?
Have any of you all designed a system in this manner where you haven't seen any condensation issues? I had planned to incorporate a safety feature into the controls to close off the cooling valve in case condensate is sensed in the drain pan of a fan coil unit which is similar to condensation prevention with the chilled beams (only they are controlled such that when an abnormal space dp is sensed that the beam chill valve would close off).
What would you recommend?
Thanks!
Antifed
I searched through existing posts and did not find a post regarding my question (though that doesn't mean that I searched very well) so please forgive me if this question has been asked and answered. If it has, please direct me to the thread.
We designed a a building in climate zone 4A, part of which is a two storey instruction facility. The downstairs portion of the facility consists of classroom spaces and support spaces (e.g. bathrooms). The upstairs spaces consists of some private offices, open floor offices, a conference room, and support spaces. The upstairs and downstairs each have a dedicated outside air system that provides dehumidified air (48-deg F dew point).
Both DOASes are partial recirculating type, have an enthalpy wheel, heating section, DX cooling coil, and hot gas reheat to temper the supply air. The downstairs DOAS supplies air to classroom chilled beams (the CB design has been reviewed by my peers as well as the chief engineer from Titus and it is considered sound) plus a couple of blower coils (where beams wouldn't be appropriate). The upstairs DOAS supplies dehumidified, room neutral air directly to the zones. The air volumes are based on providing ASHRAE 62.1 compliant ventilation airflow rates plus additional air to provide dehumidification of each space/zone (e.g. an office may only need 20-cfm of outside air, but may need 60-cfm of 48-degF dew point air to account for the latent load).
The facility will have an air barrier and non-operable windows. The space design conditions are 78-degF DB & 45%RH. A design infiltration rate of 0.1-cfm/sf of wall was used (based on ASHRAE Fundamentals for typical new construction) so the amount of air supplied to spaces for dehumidification takes into account any latent load from infiltration.
All that being said, the design did not include condensate piping for the upstairs' fan and blower coils based on the DOAS dehumidification. The building is under construction and the contractor has submitted an RFI regarding condensate piping (i.e. "it's not there, what do you want me to do?"). This is my first major design where I did not include the condensate piping based on having confidence in the design. But now that the question is being raised, I am having second thoughts. Our commissioning specialist doesn't have the warm and fuzzies and would feel better having the condensate pipe installed via a change order. I would certainly have the warm and fuzzies if we installed the condensate piping, but then what would have been the point of decoupling the latent and cooling loads with the DOAS (I ask rhetorically)?
Have any of you all designed a system in this manner where you haven't seen any condensation issues? I had planned to incorporate a safety feature into the controls to close off the cooling valve in case condensate is sensed in the drain pan of a fan coil unit which is similar to condensation prevention with the chilled beams (only they are controlled such that when an abnormal space dp is sensed that the beam chill valve would close off).
What would you recommend?
Thanks!
Antifed
