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Joined on November 26, 2011

Last Post on September 1, 2014

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Direct Digital Control

@ August 18, 2014 7:18 PM in Programmable Automated Controls (PAC) for Integrated Systems

is the industry term for this, and the better systems feature fully programmable everything.

If you hired me to do this, I would use a BACnet platform from

If you want to do this yourself, you have a bit of a learning curve ahead of you but there are quite a few options.  You might take a look at

Assuming you intend to market this system to the public, you will want to simplify both the system design and the controls.  That's not always as easy as you might think, but it is a rewarding process.

Oversized mod/cons

@ August 18, 2014 2:21 PM in Is 100k BTU the right size of boiler (or HTP heater) for both baseboard heating and indirect DHW

short cycle just like an oversized conventional boiler.  Even though there is a bit more headroom thanks to modulation, a low minimum firing rate will lead to longer run times and a happier boiler.

ROI will always be longer with a small load.  The added comfort and safety a mod/con provides may be worth a few extra bucks even if the hard dollar payback is less than optimal.

The HTP designs add mass, which is great -- just wish they made one with a smaller burner.  I could sell a 60-80k model all day long around here.

Water chemistry depending, probably...

@ August 17, 2014 10:36 PM in open loop geotherm question

If the only major issue is hardness, then your assumptions are most likely correct.  Should that be the case, A couple of hose bibs and 3-way valves and some simple routine maintenance can easily resolve the issue.

And don't forget

@ August 17, 2014 1:38 PM in Is 100k BTU the right size of boiler (or HTP heater) for both baseboard heating and indirect DHW

that your 77 feet of baseboard will top out around 40,000 BTUs per hour no matter what boiler you install.

Do not add the DHW load to the heating load -- they rarely coincide with each other and the newer boilers handle the switchover and switchback seamlessly.  Any of the boilers I listed above will outperform your existing 50 gallon gas water heater using a 40 gallon indirect -- most would using a 30 gallon.

Automated windows, shades and blinds

@ August 16, 2014 6:45 PM in System's Architect

have come a long way in the past 30 years or so.  Prices are still fairly high -- north of $200 per operator last time I used them on a job.  With proper control they can really work wonders - opening first floor windows at night when the whole house fan turns on, directing evaporatively cooled air to specific rooms while keeping it out of others, and of course shading control.  Most run on small DC motors that only draw a few watts.  ECMs really make the most sense for high duty cycle applications like fans and pumps.

Demand start of pump

@ August 15, 2014 1:43 PM in TT Smart 80 & Prestige Solo 110 Summer Gas Usage

Can be triggered by a button press (on the way into the bathroom or kitchen) or using an occupancy sensor (easiest way is to power the pump from one of the light circuits and use the occ sensor to do both jobs at once, but there are other options as well.)  This way the pump only runs when you need it and shuts off once the aquastat trips.

Thermal mass is a good thing

@ August 15, 2014 1:24 PM in System's Architect

and I'm not suggesting you reduce or remove any of it.  I am saying that when you embed your emitters in the thermal mass, the system becomes much harder to control. 

The most common problem we see is overshoot from winter sunshine.  If you pour heat into that slab at 4:00 AM to keep it (and the room air temp) at setpoint, the morning sun will come in and raise the space temp.  When you turn off (or throttle down) the heat source, the effect will be delayed by several hours due to the thermal mass, resulting in baked occupants.  We have developed mitigation strategies for this (moving OAT sensors to the north end of the east wall to anticipate the solar gain, embedding slab sensors where AM sunshine hits them first, etc.) but the best answer is to separate the emitters from the mass.  This gives you far greater control authority, increasing both occupant comfort and energy savings.

That 5ºF differential

@ August 15, 2014 1:11 PM in TT Smart 80 & Prestige Solo 110 Summer Gas Usage

on the aquastat is a big part of your issue.  You might look at a demand-based trigger to start, then allowing the aquastat to turn the pump off once the water arrives.

Surge Protection

@ August 15, 2014 10:19 AM in UPS or Surge Protection - Condensing Boiler

as an industry has a bit of a reputation issue.  There's so much hot air out there it's amazing anything works at all without thousands of dollars of exotic voodoo plugged into it.

Brickwall looks like a power conditioner along the lines of which do a great job of removing all sorts of noise, but you still need something at the service entrance (think big MOVs, SOVs, gas tubes, etc.) to catch the big ones before they get inside.  Same thing with big disruptors on site.

Zoning with the sun

@ August 15, 2014 10:01 AM in System's Architect

is how we prefer to manage things.  We also zone for wood stoves, large western exposures, and intermittent occupancies (guest rooms, workshops, etc.)

Proportional zone valves will be critical, especially if you elect to leave that tubing in the slab.

I would prefer to put the cooling tubes in the ceiling

@ August 15, 2014 9:58 AM in System's Architect

However, that would be costly.


Your design seems to be a cost-no-object approach to extracting the last 3-5% of possible energy efficiency from a dwelling.  While this is a noble and quite interessting goal, it is not cost effective by any stretch.

Pareto Principle still seems relevant to the world most of us inhabit.  Spend another couple bucks a square foot, move your tubing out of the thermal mass, and you'll end up with a much easier to control system.


@ August 15, 2014 9:48 AM in Homeowner replacing gas with electric, seek input

Nice boilers, but no ODR under 10kW (unless something changed recently.)

PEX sizes

@ August 14, 2014 1:18 PM in System's Architect

First off, 7/8" is not a standard tubing size -- most of it seems to be sold by a certain online supplier with a penchant for questionable designs and a propensity for lawyering.

In North America, PEX is sold in Copper Tube Sizes - the nominal size refers to the outside diameter of the pipe, and the inside determined by the SDR 9 standard.

For residential scale radiant, 1/2" tubing is by far the most common size used.  Conventional wisdom recommends 300' loop lengths, but even those have higher head losses than we prefer to work with.  Like high R-values, low friction is a gift that keeps on giving, saving you a little bit of money every hour of every day your pumps are running.  I try to keep my loop head under 4 ft, which allows me 0.5 GPM on 100' 3/8" loops or roughly 0.8 GPM on 150' 1/2" loops.  Either is short enough to put small rooms on their own loop, which allows us to balance the system much more easily than longer loops will.  3/4" PEX is ideal for larger spaces like warehouses and commercial garages, but in general the smaller the room, the smaller the tube size we need.  3/8" PEX is easier to install than 1/2", and we find 100' loops to work best on many of our projects.  If you're doing a dry floor system, 3/8" also allows a slightly lower floor profile.

Why will longer loops allow a lower ∆T?  In my book, they generally result in difficult to balance systems that require far too much pump head.


@ August 14, 2014 1:39 AM in Is 100k BTU the right size of boiler (or HTP heater) for both baseboard heating and indirect DHW

Your heat loss of 31k is smaller than any modulating condensing boiler currently available in North America.  Time to look at minimum instead of maximum firing rates.  My current rule of thumb says you should look for a boiler whose minimum firing rate is about one third of your design day heat loss.  Here are the options I know of with minimum net outputs [in square brackets] under 12k (maximum rates in parens):

Viessmann 200-W B2HA 19   [11,580]    (64,655)
Lochinvar WHN055                [10,450]    (53,250)
Dunkirk DKVLT-050                [10,000]    (50,000)
Lochinvar Cadet CDN040         [8,545]    (37,600)

A higher maximum rate will provide faster recovery for your indirect.  I would upsize the indirect long before I specified an oversized boiler.  Keep in mind that most gas water heaters have net outputs of 30k or less, so any of the above should outperform the old tank.

Small canister-like buffer

@ August 13, 2014 11:35 PM in Gas drip leg/reservoir

would no doubt have to be listed.  Any reason a 4" x 24" nipple with some reducers on each end wouldn't work? 

Sunvelope collector

@ August 13, 2014 6:34 PM in System's Architect

Design looks interesting,  No spec sheets on their site that I could find, but they just got OG-100 certified so we have the performance data.  Looks like they perform pretty well at low ∆Ts, but performance falls off pretty severely as the ∆T increases.  Not so good for cold climates.

The system diagrams look fairly conventional.

What are you actually trying to accomplish with this system?  Is it a research project?

Gas Exchange Analysis

@ August 12, 2014 1:35 PM in Heart attack

is kind of an enhanced treadmill test, where they measure your O2 uptake and CO2 output -- from which they can determine your basal metabolic rate, max O2, and a few other tidbits about how well your entire heart/lung system is doing its job.  Fairly popular in sports medicine and gaining traction for detection of heart disease

This is even slicker than the machine I was tested on a few years back

Gas exchange analysis

@ August 12, 2014 9:29 AM in Heart attack

is a good idea (assuming your doctor is equipped for that.) 

Thermolec B-6TMB

@ August 12, 2014 9:20 AM in Homeowner replacing gas with electric, seek input

Has almost twice the output you need and should cost less than $1,000 including shipping.  It has essentially zero head resistance at the flow rates your garage will require.  It pairs perfectly with the little B&G ecocirc e3-4 Vario, which will draw under 10 Watts when running.

You don't really need an indoor thermostat, but if you install one, it should be used as a high limit controller (set 3-4ºF above the desired space temp once the ODR is dialed in.)  Leave the stat at its maximum setting during the process.


@ August 11, 2014 10:23 PM in System's Architect

If this is similar to the SolarZentrum design, it combines an unglazed thermal collector with PV.  This creates a very efficient thermal collector at low ∆T conditions at the cost of severely limited output at low ambient conditions (winter.)  The upside is that the unglazed collector allows night sky cooling during the cooling season, which (with proper controls and buffering) could well eliminate the need for refrigerated cooling in the Boise climate.

Start here

@ August 11, 2014 8:21 PM in Books/Manuals on 3 phase electric and then follow a few of the links at the bottom.  LMK if you want to dive deeper into a particular area and I'll see what I have on file.

I'm curious about the project

@ August 11, 2014 9:46 AM in System's Architect

most particularly the overall ROI.  Is this actually going to get built with someone's hard-earned money?  I've worked on several sub-20k heat loss designs recently and we couldn't even come close to justifying the cost and complexity of a heat pump in our high mountain southwest climate (similar to some parts of southwest Idaho.)  With good passive solar orientation, R30 walls, R50 roof, and commodity double pane windows (well below Passivehaus standards) an electric resistance boiler costs about $1,000 to buy and about $50 per year to operate.  Even the cost of putting the tubing in the slab was marginal, but we and the owners both felt the future options of alternative heat sources and cooling made it worth doing.  We didn't even bother with active solar space heat in the first phase, just DHW preheating (with a single flat plate collector and pressurized drainback, simplest system we know of.)

I'd love to design and implement the controls on a project like this, but it would take a special client for sure.  Tekmar makes nice stuff, but for anything complex we find that fully programmable DDC usually costs about half what a fully-loaded multi-module Tekmar system will.

I'd suggest you take a serious look at your plan to embed emitters in the building thermal mass.  We try very hard to avoid that whenever possible, and strongly prefer a high mass building paired with low mass emitters.  If you do embed in concrete, stay away from 7/8" PEX (long story behind that particular nonstandard product, BTW.)  I usually suggest 3/8" PEX with 100' loops, giving more precise control over slab temps and making an easy job of tube installation.

Best of luck with the project -- it is quite interesting.
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