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1.  Bosch TA line fan speed

Posted 01-11-2018 17:03
Edited by Richard Clemenzi 01-12-2018 08:17
  |   view attached
We inherited a customer with a Bosch TA Series GHP that apparently comes programmed with only a single ECM fan speed - FULL.

If you know of a fan motor programmer and the procedure for fixing this, please let me know.

Rick Clemenzi, PE, CGD
Geothermal Design Center Inc.
Asheville Geothermal Inc.


Bosch TA-Series IOM.pdf   1.80MB 1 version

2.  RE: Bosch TA line fan speed

Posted 01-12-2018 07:00
This may or may not help.
If the Zone Loads are close to equal. You can set your dampers to not fully close when any zone is not calling. If the dampers are 2-wire. If they are power open power closed change dampers?Create leakage. As long as the stats are set similar. Dampers can be set then for noise control as well ?
I do this to avoid any bypass.
If the home type allows. Honeywell has a modulating automatic damper with a static pressure sensor mounted on the unit Supply Plenum. You would need a dump zone. This could replace or supplement leakage.
I have not had any problems with over or under Conditioning with creating leakage with dampers not closing fully.

Ron Newcomb/AirMasters HVAC Inc.

3.  RE: Bosch TA line fan speed

Posted 01-15-2018 08:06

What we have been installing on zone systems with smaller zones is a controller (by Jackson Systems) that will partially open closed zone dampers in response to an adjustable duct static pressure control. We will have the smallest zone calling (only) and adjust the controller by air noise in that zone. So far we have not had any complaints of overheating or over- cooling any zones. We have installed these controllers on different zone systems all you really need is 3-wire zone damper motors. It also will work on anybody's unit single or dual capacity.


Mike Hadley CGD CGI

4.  RE: Bosch TA line fan speed

Posted 01-17-2018 09:24
I'm sorry for the delay in responding. Perhaps it is too late to help you on the situation.
 I am wondering if you are using a zone controller that can actually control the heat pump based on percentage size of the zone itself. What I mean by this is that a percentage zone controller can say if only one zone is calling it will not allow the unit to go beyond low speed for that zone no matter how much demand the thermostat has for that zone.  If the zone control that you are using will allow the heat pump to run on high-speed for just one zone, that is your problem. It is difficult to have all of your zones in a house big enough to accept the entire output from the unit to any one zone.  After all, the unit is big enough to do the entire home all at once. That is why we have multiple speed units.  If your zones are too small for low-speed output from the unit to comfortably be pumped into that area then you need a variable speed unit.  To properly design an HVAC system for a home we must consider the size of the zones before we choose our equipment and our zone controller.  Bosch is giving you some options for your unit which basically are 350 CFM's per ton at factory set up or you can subtract or add 15% to that. The manufacture is simply trying to protect their equipment by not allowing you to run less air than 305 CFM's per ton.  Less CFM's than this makes the unit inefficient and can damage the unit so why would you want to go lower than this?  While dump zones and bypass dampers can also alleviate the high air noise problem, they're actually taking our very efficient equipment and making it less efficient and bypass dampers can actually cause damage to equipment due to temperature limits being reached all the time.

 Good luck with your project.
Brian Shimp
Technical and Training Director
JK Mechanical Inc

Brian Shimp

JK Mechanical, Inc.
Willow Street PA

5.  RE: Bosch TA line fan speed

Posted 01-12-2018 07:25
Try Dick Peters with the "Fan handler" company @ ​ or 877.522.5151 he may be able to help you

Bryan DeJong

Baxter Comfort Solutions
Baxter IA

6.  RE: Bosch TA line fan speed

Posted 01-12-2018 12:17
​Rick - Sorry to hear of  this, but unfortunately I have had similar experiences with other brands some years ago with 2-speed compressors and ECM variable speed (supposedly) blowers.  One maker advertised their product touting its ECM capabilities and suitability for zone ducted installs; when the unit arrived our installation crew found that the ECM place on the control board for the blower settings were sealed and the unit would operate only on high speed!  Same response from the manufacturer's so-called technical support person that you got - was not intended to vary speed and no one else had ever complained!  After climbing the company's 'food chain' finally found someone in charge and after explaining the situation, this senior person said they typically did not have people using their product in this manner!  I pointed out their marketing and technical literature said differently.  For this particular project we ordered another unit from a manufacturer with a "real" ECM blower equipped unit that actually allowed tuning max fan speeds per stage; we could have customized our own control board from our controls group but did not want the liability should there be an issue later so chose not to be married to this offending heat pump.  We dropped the problem brand shortly thereafter as they had other issues that the manufacturer would not help resolve (with new ownership this maker finally got their act together a few years later to their credit).

We have also found similar conflicts with other makers of heat pumps, so this is not a problem unique to Bosch.

[Terry] [Proffer] [Geothermal Manager, CGD]
[Major Geothermal]
[Wheat Ridge] [CO]

7.  RE: Bosch TA line fan speed

Posted 01-12-2018 13:01

I think I might be confused with what you are trying to say. Of course there is only one full load speed. The TA is a dual stage unit so you should have "fan only" 1300 CFM, "partial load" Y1 @ 1500 cfm, and "full load" Y2 @ 2100 CFM. This is on page 8 of 32 on the IOM. So technically, you have 5 speeds: fan only, part load, full load, Adj-, Adj+
Does the Thermostat have Y1,Y2 or just Y1? some older stats dont work with staged units.

W. Blake Smith

Sound Geothermal, Inc.
Sandy UT

8.  RE: Bosch TA line fan speed

Posted 01-14-2018 23:16
Thanks to all for your input.  We are replacing the zone damper motors with ones that are more reliably adjustable for min % open.

But, I am really hoping that someone from the manufacturer will realize the error and loan us a motor programmer to reset the max speed ... even a lower single max speed.  Anyone who has installed residential systems knows that max fan speed adjustment is part of the normal startup sequence.  I am convinced that several manufacturer's engineering staffs have never used their systems in residential settings ... and that is not just this mfgr or this issue!

For those who do not know, some/many HVAC and GHP manufacturers ship all their ECM AHU's with 4 fan speed options for heating and 4 for cooling.  As it happens, I cannot remember a single residential system where the "full" speed was the one we ended up using to best fit the home and provide a quality, quiet installation.

Rick Clemenzi, PE, CGD
Geothermal Design Center Inc.
Asheville Geothermal Inc.