Aprilaire 8800 in an existing 8870 system

wilw410

I have a client who is expanding their system. The expansion will add three new thermostats. All we were able to order were 8800's because the 8870 is now unavailable. Has anyone used 8800 and 8870's side by side in the same system? The protocol docs say the 8800 protocol is the same with additions for scheduling. FYI, I am using the duet module for the AMX Viewstat to control the 8870's and hoped to just add the 8800's to the distribution panel with new addresses.

vining

wilw410 wrote: »

I have a client who is expanding their system. The expansion will add three new thermostats. All we were able to order were 8800's because the 8870 is now unavailable. Has anyone used 8800 and 8870's side by side in the same system? The protocol docs say the 8800 protocol is the same with additions for scheduling. FYI, I am using the duet module for the AMX Viewstat to control the 8870's and hoped to just add the 8800's to the distribution panel with new addresses.

Have they published the amended protocol? If you're using the duet mod you may be able to adapt the code by using the pass back and pass thru commands but you will have to make these modifications to use the new control commands yourself.

mpullin

Do you need to invoke the scheduling? If not, you are done. Just add the 8800s to the bus in the standard way.

John Nagy

The 8800 documentation in fact shows how to wire a mix of 8800's and 8870's to the same distribution block.

Have they released documentation for schedule protocol? When we last asked, they said it was not planned for remote control. Seemed short sighted but that's what support was saying. Hope it has or will change...

FYI, I'm told the process for setting the device address is different, but nothing else about it... this is second hand but trusted....

vining

mpullin wrote: »

Do you need to invoke the scheduling? If not, you are done. Just add the 8800s to the bus in the standard way.

If they're to be used remotely with in room sensors that would be ok but if they're being installed in the room they serve then you have potential user issues. They may enter program mode, place on hold, etc. the price is about the same if I recall but they can potentially create problems. Personally I prefer the stats to be remote with sensors in to rooms but sometimes that's not an option.

wilw410

The programming document has been released. It contains the commands for scheduling.

DHawthorne

Well, that's a step up because their 8870 programming manual that was available online was a bad scan, and much of it was illegible. I reported it to them years ago, and it never got fixed. The temp/humid control commands, and feedback, look to be the same, so it should be backwards compatible.

sonny

Has anyone got this working yet? I get nothing but a stream of junk back from the 8800's. Have tried both direct connect to Netlinx port and through an 8818 where these replaced 8870's (2 replaced are sending junk, but I can cut them off and the 8870's communicate fine). Almost seems like a wiring issue. I know I've had instances where I had to hook the REF line up to get solid communications with an 8870 direct to the Netlinx port, and there isn't a REF connection on the 8800.

HARMAN_icraigie

Getting a system online full of 8800's as I write this - looks like a couple of bad devices out of the box, the instant they are put on the bus the serial port is choked with gibberish.

vining

sonny wrote: »

Has anyone got this working yet? I get nothing but a stream of junk back from the 8800's. Have tried both direct connect to Netlinx port and through an 8818 where these replaced 8870's (2 replaced are sending junk, but I can cut them off and the 8870's communicate fine). Almost seems like a wiring issue. I know I've had instances where I had to hook the REF line up to get solid communications with an 8870 direct to the Netlinx port, and there isn't a REF connection on the 8800.

Yeah it kinda sucks that these now power off the individual HVAC systems, typically the air handler power and you can't power them off a common xformer that can be controlled and remotely cycled when/if they lock up.

I was looking at the manual and it says the dist panel is a model 8819 so maybe its different than the 8818 of old. Maybe that's part of your problems if your still using the 8818? I just wired for a new install but haven't yet played. Hopefully these bugs will be resolved by then. I hope!

edit#1
I would assume that you can't mix T-Stats either so it's all of one or the other on the proper dist panel unless you use 2 serial ports and connect one to an 8819 dist panels while another serial port talks to the 8818 dist panel. I would have naturally assumed that you could just pull out an 8870 and replace it with an 8800 but it doesn't appear to be the case.

edit#2
Ok reading down to JNs post I found they do provide for a combination of 8800s and 8870s wired to an 8818 dist block so forget everything I just said!!!!!!!!!!!!! Just scrolled down further in the install manual and it shows what JN says it did. Still no ref though or ability to power the T-Stat from the common supply.

sonny

I've got a response from Aprilaire coming, this appears to be a pretty serious issue. I'll post more info as I get it.

DHawthorne

Here we go again. Aprilaire promises a fix to their most egregious problems, and the solution is worse than the original problem. Not the first time.

sonny

It appears to pertain to some sort of Common issue when powered off the HVAC transformer. The comms in the 8800 still work under battery only power, so when I disconnected R & C I could communicate with the stat fine. According to Aprilaire this is an ongoing issue with a number of HVAC manufacturers. The attached drawing is their recommendation. I've ordered an Aprilaire 8024 relay kit to see if that fixes the issue.

DHawthorne

I've talked to the engineers at Aprilaire, and I got one to admit that there is insufficient isolation between the signal common and the power supply ground. So if there is any kind of noise on the power line (and frankly, how could there not be with a simple 24VAC transformer on the furnace?), some of that noise could be spilled over on the stat's comm circuit. Now this was with the 8870 ... and I would gather they didn't fix it. My solution was to never power the thermostats from the furnace supply. I have seen stats flip out right in front of me, when nothing happened except the HVAC guy turned on a bypass switch to power the furnace. How you could possibly even think you can run electronics cleanly with that type of supply, I just can't figure.

vining

sonny wrote: »

It appears to pertain to some sort of Common issue when powered off the HVAC transformer. The comms in the 8800 still work under battery only power, so when I disconnected R & C I could communicate with the stat fine. According to Aprilaire this is an ongoing issue with a number of HVAC manufacturers. The attached drawing is their recommendation. I've ordered an Aprilaire 8024 relay kit to see if that fixes the issue.

Why didn't they build this isolation into the t-stats? It's mind boggling! Didn't they test before production?