Electric Boilers

Air-source heat pumps and VRF systems have signficant capacity limitations and are not going to perform well at colder ambent temperatures.  The major boiler manufacturers all offer electric resistance boilers. . . but the electrical feeds get really large (eg 360A@480v/3ph, 300KW for a 1MBTU electric boiler) and right now I do not think electric boilers are specified very frequently.   I keep wondering if smaller electric resistance heating elements in VAV boxes, fan coils, etc. are going to make a comeback in an electrifying world. No refrigerant, no hydronic piping, no standby losses, 99% conversion efficiency. . . although electric resistance has been viewed as a poor energy choice in the past and on paper is a lot less energy efficient than a heat pump or VRF system.

We've learned on a few projects to use a condensing gas boiler as the backup to a heat pump (typically air source) rather than an electric boiler.  Electric resistance is far worse in emissions per unit of energy than a condensing boiler in most grid regions (currently).  In order to provide code-required minimum heating to prevent damage from freezing, designs with electric resistance boilers require larger generators, which can get very expensive very quickly.  Our carbon emissions analyses of a New England lab project with ASHPs as the primary heating source showed that the carbon emissions delta between an ASHP backed up by a gas boiler vs. backed up by an electric resistance boiler was negligible because the gas boilers only ran for ~200 hours/year, and the gas backup option cost less overall.  Plus, as leaned in Texas this winter, having redundant fuel sources can make a design more resilient.  Sarah, I'm happy to nerd out about this in more detail with you offline. :)

I would add to Patrick's response that we should all be taking a serious look at alternatives to gas, even for back-up.  For example: fuel oil may be a better solution because the gas utility infrastructure is becoming a stranded asset.  With dwindling consumption and a lot of back-up capacity required, on-site storage may make more sense.  We are seeing some utilities levy huge back-charges to extend or increase gas service to a site, particularly for uses like standby generators...the utilities will likely have the same reaction when it comes to back-up boilers in the near future.  What do others think?

Agree with all the prior comments.  This is a regular question/discussion in NY.  In the North East we have seen electric boilers looking 1.5 - 2 times worse on Carbon than natural gas boilers. I have also seen an impact on electric infrastructure on the order of 50% - 60% higher HVAC peak load with electric boilers (compared to gas heat).  There is concern that banning natural gas in the North East could push folks to electric resistance for the full system, which would be higher Carbon emissions in the short/near term. Recently I have been looking into the idea of an electric boiler boost on a air-to-water HP loop to limit the heating capacity of the HPs needed (the way I have been thinking about it is X BTUH at say 10 or 15F Outdoor Air, which is X-Y BTUH at -5F OA and putting in a Boiler to cover that "Y" capacity. Meaning, we design for the extreme (-5F) but that condition maybe only happens a handful of hours.  I think this is consistent with what Patrick and Jacob describe. Always happy to discuss more... its a constant topic here.

Hey Jeff, What emissions factors are you using for natural gas when comparing to the electric boilers? We've started talking a lot about natural gas leakage (see the NYT Article). Loosing just 3-percent of the total NG extracted from the wells bring NG emissions equal to coal. I realize too that accounting for this will impact electrical generation emissions depending on how much gas is in the fuel mix. In the PNW, it's still impactful enough to change many of the calculations in favor of electric-based heating, especially given the near-term plans for greening our electrical supply. Marc Brune, PE, LEED AP PRINCIPAL PAE d: 503.542.0520 Get connected

Great point Marc, and you are right to call me out on it.  Generally speaking I am using a simple and blunt (dumb?) metric.  Most often, in NYC specifically using the Local Law 97 emission factors (those are below).  We are in some ways necesarily thinking that way due to the law, but I am not sure it captures it all.  In other areas I default to EIA info (probably even less accurate).  Also, shout out to Jacob who was bringing up the natural gas leakage issue 2 years ago at the first SMEPL summit...  My question is, how do we get an accepted metric for it?   NYC Local Law 97 Emissions: Utility Type Greenhouse Gas Emissions Equivalent Conversion Values (tCO2e/kBTU) Utility Electricity 0.000084690   Natural Gas 0.000053110   No. 2 Fuel Oil 0.000074210   No. 4 Fuel Oil 0.000075290   District Steam 0.000044930    

Love this conversation.  Taking it a different way (away from carbon - to cost), we are in progress studying a new 1.2M sqft tower (70% resy; 30% office) and came up with the following energy cost results.  Keep in mind, this is based on NYC utility tariff prices and all schemes include the best-of-the-best in terms of efficiency systems, envelope, heat recovery air distrubution (doas), etc. Central Plant Schemes: ASHP heating; chiller plant cooling:  $1.90/sqft Electric boiler heating; chiller plant cooling: $2.59/sqft Gas boiler heating; chiller plant cooling: $1.78/sqft Steam heating (utility steam); chiller plant cooling: $2.39/sqft   Best Chris  

Switching gear to embodied carbon and EPD discussions.   While efficient in COP, Air source heat pumps can be impactful in resources depletion and life expectany impact in environmental declaration, and the refrigerant can have embodied carbon impact for a long time (refrigerant leakage is embodied carbon "B1" category in EN 15978).  While electric resistance heat and gas boilers have no refrigerant.  The below article in 2012, compared Air Sourced Heat Pump and found it is wose than Condensing Gas Boilers, though the fossil fuel electric grid has much to do with it.   https://www.escholar.manchester.ac.uk/api/datastream?publicationPid=uk-ac-man-scw:178995&datastreamId=POST-PEER-REVIEW-PUBLISHERS.PDF

My experience is limited, but I did look into them for a project very recently. They require a 50F delta T and if you try to violate that the COP drops to 2 in a hurry. They also are not allowing their product to be used in any application other than domestic hot water (mechanical heating hot water is not allowed currently). I think they want to be heavily in control of the success stories of their product as it first hits the market. The system also comes with all components provided by Lync except the storage tanks, so it is partially turnkey (for better or for worse). I also looked into an offering from Mitsubishi (through their partnership with Trane) that has exactly the same restrictions on use and performance. Since I was exploring an industrial hot water application I was not able to proceed with either CO2 heat pump, but made a note to explore them again on my next project with residential domestic hot water. Trane is not advertising their Mitsubishi offering for the US clearly on their website. I encourage you to reach out to your Trane Rep for more information. Hope this helps. ________________________________ Noah Zallen | Principal Integral Group | Trust | Nurture | Inspire P: 510.663.2070 x 2066 | M: 508.272.5543 integralgroup.com | nzallen@integralgroup.com 427 13th Street, Oakland, CA 94612 | Register Now! IG|VISION From Analysis to Reality: Bridging the Zero Carbon Procurement Gap ​This email may contain confidential and/or privileged information. If you are not the intended recipient or have received this email in error, please notify the sender immediately and destroy this email. Any unauthorized copying, disclosure or distribution of the information contained on this email is prohibited. Ref A524GE65 F