Classromm IAQ

[reftec021702]

Dear fellows:

I just finished the installation of some ductless mini split systems in a local elementary school. Everything working fine so far. Now, some school members are worried about flu transmission due to air recycling. Any idea on how to provide some additional sanitation to the air inside besides proper unit maintenance? Any suggestions welcome.
Thanks!!

 

[GMcD]

Not much you can do with those unless you try small UV-C germicidal lamps at the air inlets (return air) area of the ductless mini-splits. The sales hype on those things sure glosses over the fact that you only have a fixed DOAS ventilation supply for that type of system- they may be fine for local temperature control but they do squat for IAQ. School classroom designs should be looking hard at low level displacement ventilation with 100% OA for better IAQ, while still providing low energy use.

 

[BronYrAur]

I'm surprised that code allowed ductless splits with no OA ventilation!

 

[ChrisConley]

What was installed before your added the mini-splits? I was assuming that this was a retrofit just to give some AC.

Unless you're using a DOAS with radiant cooling, as GMcD recommends, all systems have recirculation.

Flu transmission through air recirc is more of an issue when you have common returns connecting multiple spaces, not when you have a mini-split in the room taking room air and swiriling it around, exactly like a ceiling or desk mounted fan would.

 

[reftec021702]

Thank you very much for all of your feedback.

I must said that the classrooms do have an independent outside air injection system, including a pre-cooling coil, which is suppose to keep proper ventilation rates. I believe that board members are more concerned about in-room flu spread, not really about cross contamination from the other classrooms. And this concern originates from the fact that the 15 year old inefficient 3-ton AHUs that used to supply air conditioning to these classrooms, had an UV lamp system installed on their ductworks. I think that these ceiling hung mini-split evaporators have some room in the return section, which can be used to install some very compact mini UV lamps? Does any of you guys know about such lamps ?

Thank you!!

 

[AbbyNormal]

Install some hypochondriac free standing or ceiling mounted air cleaner for the pyschological peace of mind

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

I'd be concerned about installing UV lamps in the inlets of those cheap plastic fan-coils- the UV lamps may embrittle the plastic parts pretty quick. I don't think you'll find room inside those little fan-coils to put a lamp and the fan-coil supplier will likely walk away from any performance issues and warrantees if you try to put something inside the fan-coils inlets.

Fundamentally, if the concern was germ-spreading, the whole air system should have been changed out to a low level displacement ventilation system using the 400-600 cfm of minimum ventilation air you have anyway (15-20 cfm per person with 30 people). Do the math- I bet you that taking the dedicated ventilation air quantity, cooling it to 64F, and supplying at floor level, will do your cooling needs while providing 100% flow-through outdoor air. If you have solar cooling loads, then use exterior shading to eliminate it, and then the only cooling load you have left is a portion of the people and equipment, since heat from the lights goes away into the 100% exhaust air stratified layer. Think about it next time you have another school retro-fit.

Local climate conditions will dictate what amount of humidification or de-humidification you'll also need.

 

[zekeman]

Where is the documentation supporting the effect of air circulation on flu spreading? It seems to me if the problem is there, you would see school epidemics more frequently.

This is not to downplay the problem, but surely somebody has studied it and result in subsequent code restrictions.

 

[ChrisConley]

I agree with AbbyNormal, hang something in the space and tell them it absorbs flu bugs. Better yet have it generate some ozone for 'scent' so they know it is working.

When's the last time you saw a UV lamp on a ceiling fan? Same idea here, you're just recirculating air in the space.