[RE-wrenches] Electric boiler usage?

[Darryl Thayer]

If this is a new house someone should have calculated the design heat loss.  Or the UA if you know the loss BTU per hour/degree F multiply by the the dgreee Days, I would guess about 10,000, then multiply by 24 hours/day 
So (heat loss(BTUh/DegreeF)xHDD about 10,000x24 h/d)= annual heat loss in BTU/yr.  I find that when the house is built most of the time this is close.  For super insulated i find many times the heat loss is higher.  
 
I have worked on some net zero houses in Minnesota.   
All the houses net zero, have a heat pump.  A heat pump will reduce the annual heating consumption to about 1/2 to 1/3 of electric resistance.  
 
Many people use the tax credit to pay for the complete heat pump installation.  BUT heat pumps are very limited in the output temperature.  The heat source can not exceed about 110 to 115 VERY Max,  higher temperature will require electric resistance.  The heat pump can heat hot water to almost 130F using what is called a desuper heater.  
 
My net zero experiance finds that the PV takes up so much space they can not affort solar thermal.  Suprizing as this may sound, PV for heat pump and heat pump for hot water and space heating.  
Darryl

From: Jesse Dahl <dahlsolar at gmail.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Saturday, August 27, 2011 2:57 PM
Subject: Re: [RE-wrenches] Electric boiler usage?

Wrenches,

I've talked to the homeowners today about the system.  They are using www.warmboard.com subflooring and are talking to the manufacturer about boiler size and load.  I'm hoping they have some data.  Im guessing they spec a boiler. Another factor we have here is dual fuel and off-peak heating rates.  

This does seem tricky!!


Jesse

Sent from my iPhone

On Aug 27, 2011, at 8:50 AM, Ian Woofenden <ian.woofenden at homepower.com> wrote:

> 
> Hi Jesse,
> 
> If your client were mine, I'd be recommending a heat pump, which would lower the electrical load significantly. It will be a larger up-front investment, but will likely have a positive economic return, and an immediate reduction in grid fossil fuel use. Whether air-source or ground-source would depend on the climate and budget. If they were willing to let go of the radiant floor delivery system, a couple of mini-splits might do the job (depending on the climate). An HVAC contractor I work with recently speced a single mini-split for a 1,000 sf home in our moderate climate -- installed cost was $1,000. I'm putting a kWh meter on it, so someday I'll have data.
> 
> I strongly recommend that you have your client add a reconditioned kWh meter (available for less than $50 from a couple of sources), so that they have a measure of actual ongoing performance of whatever heating system they decide on.
> 
> Projecting your electrical usage for boiler or heat pump will be tricky, since it will be based on your heating degree days and the overall R-value of your house. Local heating contractors _should_ be able to give you an estimate based on generalized tables. Sometimes they only work in dollars, but converting to kWh is easy. But I don't think their estimate will be specific to the heat gain/loss of that specific house, but just based on an average and the cubic footage.
> 
> I'll be interested to see what decisions are made and how it plays out.
> 
> Ian
> 
>> Wrenches,
>> 
>> I am working with a family that wants to install a grid tied system that will offset, as close as possible, 100% of it's electrical usage.  We have calculated for almost all the loads except the electric boiler. 
>> Problem, they don't know which boiler they will be using. The home will be 1800sq ft, it will have the in floor heat between the floor joists and the joists will then be insulated with foil-faced insulation. 
>> Has anyone calculated a boiler like this out for annual electrical usage?
>> 
>> 
>> Thanks as always,
>> 
>> Jesse
> 
> -- 
> Ian Woofenden <ian.woofenden at homepower.com>, Senior Editor, Home Power magazine
> Subscriptions: $24.95 per year PO Box 520, Ashland, OR 97520 USA 800-707-6585 (US), 541-512-0220
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