IMO Priority Hot Water in Cold Climates is a Waste

[Deleted User]

And it is done for a reason. I have many orphan customers who found out the hard way, that waking up to a shower temperature just slightly lower than 8 hour old urine is NOT a good way to start the day.

If the physical plant was oversized to handle the combined loads of showering AND space heat, it is grossly oversized and will short cycle like a banshee during partial loads, thereby wasting copious therms of energy.

In your case, I suspect a scaled up heat exchanger in the transfer process, because 40 minutes is a long time to be waiting for the heating system to come back on.

Another option would be so get rid of the indirect, and get a reverse indirect which holds a lot less stored water and reacts much quicker on the heating side of things. A word of caution here, if you don't have a modulating/condensing heat source, you may have to add a thermostatic valve to keep your appliance from turning into one (condensing boiler).

But trust me, in most cases, DHWP is a neccessity, not an option.

ME

Chris Williams_6

This has only become apparent but this week has been below 20 degrees every day. So here is the scenario again, basically we get up the house is like 62-65 (manual thermostats) we take showers and have turned the heat up before we went in, anyways after we come out, I go into an area that we didnt turn up the thermostats (3 zones) its like 60, and oh well the heat wont even try that zone until the HW is satisfied, just cranking and circulating away, only fires the boiler when it hits the low, instead of cranking all the zones incl the HW that are calling and give me SOME heat. So basicalyl I wait about 40 minutes to get some heat. I just dont get why this would ever be a good system except where HW was your only priroity, but the real problem is the hot waer transfer of the HW tank is slower so as it runs closer to the low limit it gets even less tranfer, so if I was heating my other zones, but burner would be firing and I would probably maintian a hotter temp basically get more heat to the HW as well as some to the zones.

Juts seems like the only benefit is saving $ for the installer, since they done need a zone relay since I have 1 circ pump for 3 zones, and 1 for the amtrol but that does the swtiching, though I must need a relay to run the other circ too.

Chris Williams_6

This has only become apparent but this week has been below 20 degrees every day. So here is the scenario again, basically we get up the house is like 62-65 (manual thermostats) we take showers and have turned the heat up before we went in, anyways after we come out, I go into an area that we didnt turn up the thermostats (3 zones) its like 60, and oh well the heat wont even try that zone until the HW is satisfied, just cranking and circulating away, only fires the boiler when it hits the low, instead of cranking all the zones incl the HW that are calling and give me SOME heat. So basicalyl I wait about 40 minutes to get some heat. I just dont get why this would ever be a good system except where HW was your only priroity, but the real problem is the hot waer transfer of the HW tank is slower so as it runs closer to the low limit it gets even less tranfer, so if I was heating my other zones, but burner would be firing and I would probably maintian a hotter temp basically get more heat to the HW as well as some to the zones.

Juts seems like the only benefit is saving $ for the installer, since they done need a zone relay since I have 1 circ pump for 3 zones, and 1 for the amtrol but that does the swtiching, though I must need a relay to run the other circ too.

Chris Williams_6

I should have also said, prog thermostats are fine, but not everything in life is planned out, like if u sleep in or get up early, and if I turn the thermostat up while using some HW for a shower, I think the bruner should do everyhting it can to actually deliver some heat to the zones calling for it, instead of just giving one that is about the slowest zone any to be satisfied.

hr

It still sounds like a system glitch, not a concept issue

priority DHW can and does work fine when all the pieces are properly installed and working.

Some of the priority controls now have "time out" features to prevent getting stuck in priority for extended periods.

If the boiler and indirect are properly sized, piped, and controlled, and your DHW use is not excessive, you should have plenty of DHW and heat.

I have a 32 gallon indirect powered by an 80K Lochinvar Knight and can get endless DHW at a shower flow, and less than 20 minutes to recover if I do drain the tank by running multiple HW loads.

This can all be shown and explained with equasions and formulas. It doesn't have to be a guessing game.

I still would bet you have a compromised HX coil in your tank.

hot rod

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Maine Ken

If you have a call for heat then your boiler should be firing towards the high limit and not dropping all the way to the low limit. What type of boiler do you have? What control? With stated low limit, it sounds as though you have a triple aquastat. What is your low limit setting? High limit setting? Differential? If you are hovering around low limit then your boiler is not giving you all it can! I am willing to bet that you have some control sequencing problems. It takes longer to heat an indirect with less btu's than it does with more.

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BillW@honeywell

Our new AQ2000 addresses that very problem...

If it senses that certain zones are getting too cold, it will override the priority, shoot 10 minutes worth of heat tothe effected zones, them go back to heating water. It's not a cure-all for a poorly designed, or undersized equipment but it will definitely help.

Unknown

I don't understand

why you wouldn't set the thermostats to heat the house before you wake up and take showers ? Oh , sorry , I just read about the manual thermostats .

Of course you can disable the priority function to keep the heat going . But it sounds like you have a few people taking showers one after another ? Is it a 40 minute wait to get heat after the showering is done or from the begiining ?

It's a damned if you do - don't situation . If you disable the priority , you run the risk of cold showers in the morning . What about buying a few programmables and setting them to overshoot to cover the drop in temp , just for the morning ?

Trust me , I'd rather walk out of a hot shower into a cool room than vice-versa .

Ted_9

TN4

Tekmar TN4 has a neat heating and domestic water priority set up. Check into it.

Massachusetts

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Joe Brix

I use a Tekmar

with a circ for the indirect and a circ for the heat side with zone valves. Even when the Tekmar's in DHWP mode, the zone vales open and you get some ghost flow so the rads are not stone cold. My 36 gal Phase III is back to 130 degrees in about 10 minutes with DHWP after a shower. I say chuck the Amatrol.

realolman

One of the problems

with electrical or electronic stuff is that it can't think, and sometimes logic doesn't seem very logical.

You know you're done showering and now you want some heat and the hot water could wait, but the controls don't. All they know is the DHW is below the set point and it needs to be heated up.

I'm sure you could install some sort of controls that would do what you wanted.

Mad Dog!!!!!!!!

Or....the dhw circ is not up to the task


Also, what is the size of the dhw piping? Dhw priority works fine whenn designed and installed properly. Long Island gets plenty cold...it was in single-low teen digits
for the last few weeks. No complaint calls. Mad Dog

Mad Dog!!!!!!!!

I agree with Ron

In any case, some nice programmable stats are a good idea. Mad Dog

Jim Franklin

Log on to your house

When I'm old and rich and flush with round tuits, I will look into computerizing the house control. Wake up, grab the bedside remote and turn on the heat & DHW. By the time I crawl out of bed both are finished. Or on those rare occasions when I'm able to/have to get up NOW (like M-F), hit the "postpone" button on the 'stat as I exit the shower which delays DHW priority until the current heating cycle is complete. Or have a flow sensor that prioritizes DHW only when the shower is running. As I leave work I www.myhouse.com and turn on the heat- living zone if it's 5pm, bedroom zone if it's 10pm. Etc.

archibald tuttle

smart controls or smart controllers?

I'd go with some cost effective bits first. Not even the most expensive controls can predict your behavior. Some bumping back and forth after not making the hotwater temp for a certain time isn't a bad compromise control strategy and sounds like Honeywell and Tekmar have implemented that (or some monitoring of rate of room rise from their smart controls), but that is probably a more expensive fix than I would consider unless they have implemented lower price structures as well.

Maybe you lead a very unpredictable existence, but barebones setback thermostats won't even run you $30 bucks these days if that would handle the problem half the week.

What boiler/zone controls are you currently using? A standard 503 with priority to run the two pumps with ganged zone valves tripping a single zone on the 503 for the heating circulator? You could just switch off the priority.

If it were a 503 exp, you could take control of your boiler temps for heating with a 700 expansion controller and then tighten the differential on the primary aquastat for the priority so you while you might get shorter cycling you could keep much hotter water available for the DHW cycle.

The main distinction on whether the priority ought to hold seems to me to be whether someone is going to take a shower after you. I used to have a little cutout switch for the hotwater mounted next to my thermostat. If you slept in and you're into setback mode and you want some heat while taking one shower in preference to DHW makeup, I just hit the cutout switch before I took a shower which stopped the hot water demand from reaching the relay. I also used it as a 'vacation' switch.

Of course the downside is if you forget to turn it on after the house warms up then you don't have hot water the next time you need it (but think of all the money you save).

I don't know if there is a good low cost NC timer switch that could substitute so you couldn't forget -- kind of like the hush switch on a fire alarm after you burn the toast. You could probably adapt a threeway 120 light timer but that would be a little bit cumbersome and they cost like 30 bucks compared to grabbing some panel switch from your last erector set project for the bubble.

Brian