Baeboard heating - VAV cooling 1

[remp]

My perimeter zone now has electric baseboard heating and relies on VAV cooling. It also has a water heater in the box for some heating.
How do I control the heating sequesnce.
I was thinking; To achieve setpoint
Stage 1 - take the box to a minimum position
Stage 2 - open reheat valve
Stage 3 - switch on the base board heaters
Will this work?
I am trying to get the baseboard heaters on a thyristor controller so as to ramp up/down the heaters.??
Has anyone installed baseboard heaters before, how did you control them?/

 

[BronYrAur]

I'm no control expert, but here are a few thoughts anyway.

Other than the cost of running electric heat, I would think the best approach would be to ONLY use the baseboard for winter-time heating. Otherwise I think the 2 heat sources may fight each other. Plus, it's always nice to have perimeter heat for windows, etc. Use your VAV coil ONLY for summer reheat. An exception to this may be for a morning warmup cycle. As far as control of the baseboard, they should have a thermostat or some other controller already.

 

[willard3]

Is this an office building?

If it is, there will have to be some method to bring in outside air (OA) and this is what the air system is good for.

Heating is a separate problem.

Heating sequence should be 2-stage with stage 2 and 3 being simultaneous.

 

[AbbyNormal]

I would vote temper the air to room temp to be neutral, and heat with the baseboards

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

 

[SAK9]

Remp,

I guess the system you mention here is the same one as in your previous post. Since such a system is uncommon, I would suggest to keep it very simple so the maintenance guys do not need to rack their brains as to how it works.


My suggestion is:

1. In winter, the VAV box thermostat should ramp it down to its minimum position( just to provide fresh air ventilation for the space).
2. Use the VAV reheater battery to heat it up to room temperature. You can use an off coil thermostat to control the heater output.
3. Use the VAV box thermostat to control the baseboard heating thru a SCR.
4. In the above system the heating is 100% handled by the base board and the VAV box only provides ventilation. So there will not be any conflict between the two systems

 

[gregha04756]

Hi remp,

The typical heating sequence I have seen, which is essentially what you stated, is:
1. Position damper for minimum airflow
2. Switch on peripheral heat (baseboard)
3. If space temperature isn't satisfied by peripheral heat only, open reheat valve (modulate it if it's a proportional valve)

I have worked with SCR and triac relays that can be "pulsed". The pulse duration is proportional to the difference between space temperature and setpoint, usually up to 10 seconds. It's hard to say how precise this pulse width modulation scheme is, but it seems to be fairly typical.

I work on programmable controllers that are normally installed in a BACNet network with a parent or master controller, running an air handling unit, that takes care of occupancy schedules, outside air, and so forth. What kind of VAV controller are you working with? Does it implement a "canned" VAV algorithm or is it programmable?

Good Luck,
Greg Hansen

 

[remp]

Greg

The BMS company told me it is programable and they can do anything sequencing.
I notice you have changed sequesnce 2 and 3 around. I think i agree with you. When the box is at its minimum switch on the baseboard heaters, then.Thanks for the vote of confidence.

regards

 

[atlas06]

Greg,
I agree with what you describe if the VAV has a low set point. If you have a high minimum set point (due to ventilation requirements such as a conference room), then you may want to have HW valve reheat before the FTR.
During summer, you don't want to enable the FTR before the reheat, because all you want is avoid sub-cooling of space from the high min. VAV setting.

Does that make sense?

 

[gregha04756]

atlas06,

Yes, makes sense to me.

Good Luck,
Greg Hansen