HVAC Math: 4 Seasons - Comfort = 1 Season?

For whatever reason I've recently had the opportunity to talk to three different homeowners in the span of a week that have comfort concerns in their homes.  That's not terribly unusual, I suppose, as the majority of people probably have at least one area of their home they're not comfortable in.  What was interesting about these is that they were all the same type of area - 4 Season rooms.  They go by many names - sunrooms, 4 season rooms, 3 season rooms, Florida rooms, Solariums, screenrooms...

The idea is the same - a space with most of the walls being windows that should ideally be a place you want to spend a lot of time.  Unfortunately, without proper temperature control what you end up with is a room that is far too hot in the summer (all that glass makes it a pretty good greenhouse) and far too cold in the winter (the best window in the world is still a pretty lousy wall for keeping in the heat).  

So what's a person to do? I've seen a few different strategies employed, even within the three that I've visited recently.  One such strategy is to tap into the existing home HVAC system in order to get some heating and cooling that you already have available.  There are a few reasons this plan typically fails, sometimes miserably.  

First - since these structures are often additions to the existing home rather than being built with the home, there is no accomodation in the HVAC design for their load.  When the contractor that builds the addition simply pulls more supply leads off an existing trunk line or other supply lead in the basement that was close to the addition they aren't taking into account how much air is able to be supplied to the area and whether or not it is enough to satisfy the load.  Remember, these rooms often have a ton of solar gain year round and tremendous heatloss for their size in the winter.  Often return air is simply neglected if running them is more difficult.  

Second - because the need for heating and cooling is so variable throughout the year and even throughout the course of a day, independent temperature control in a room of this type is critical.  If the thermostat that controls the home HVAC system is in the middle of the rest of the house and it is a mild, sunny day, the system will have very few calls for heating or cooling but the sunroom could be baking hot and will stay that way until the sun goes down.  

In one of the homes I visited, they had this situation and it made the room unusable.  The existing trunk that was tapped to feed the room was sized to handle supplies in the kitchen and a small bathroom on one end of the house.  With two additional 6 inch supply vents pulled from it, at best the Sunroom was getting a gentle breeze, and the Kitchen and bath were getting less than they should have as well.  The sunroom has been comfortable for at best a few hours of some days, it is otherwise too hot or too cold.  Remember all those wonderful windows to enjoy the natural light?  Shuttered off almost completely to minimize the greenhouse affect and an electric space heater was brought in to extend the usefullness (at the cost of high electrical usage) of the space in winter months.

Other strategies involve the use of supplementary heating or cooling through the use of portable equipment - usually electric space heaters (like above) and floor or window mounted air conditioners.  All of these are expensive to run and many are noisy and potentially dangerous for children and pets. In addition, window air conditioners pose a safety and security hazard - they can be very heavy and should be taken out during the winter months when they're not being used.  There is also a security concern when the window space they are installed in is not able to be closed or secured as well as others.

Another potential solution is something called a PTAC unit - sometimes called a Hotel unit.  You know the type if you've stayed at just about any hotel - they're about 4 feet wide, 2 feet tall and they are all pretty loud and aren't exactly designed for longevity.  They are effective at heating and cooling a space, but they're not very efficient and have some compromises in order to keep costs low. 

So what solutions do we recommend?  It depends.  It depends on your current HVAC system, how it is configured, how big the Sunroon is, what orientation it has to things like morning and afternoon sun, how well it is sealed and insulated, etc.  The goal for us is always comfort and efficiency and our solutions are engineered to meet those needs for the minimum cost.  That's why conducting a complete heat load calculation is essential in solving this comfort problem.  One potential solution is to add zoning to your existing system.  Zoning is a system that enables your existing HVAC system to independently serve multiple areas of your home the amount of heating or cooling they need.  Zoning adds thermostats to different areas and through the use of a zone control panel and mechancial dampers within the ductwork is able to deliver warm or cool air to the areas of the house that need it at any given time.  Rather than a single thermostat controlling the equipment for the entire house, each zone can now ask for heating or cooling while the other zones remain unchanged.  

So, if it's a sunny but mild day, most of the house will not likely need cooling, but the sunroom may as the morning sun comes through the windows and heats up the space.  With zoning, the AC can come on to cool the sunroom while leaving the rest of the home unchaged.  Zoning can be a cost effective way to add the temperature control needed to make a space comfortable, but it does require proper ductwork to be connected to the addition as well as have a sufficient load to avoid short cycling the equipment when it is the only area calling for heating or cooling.  In other words, you don't want your 5 ton air conditioner coming on to cool a room that only needs 1/2 a ton of cooling.  So while zoning may work well for some folks, it's not an option for others.


So what about those others?  The people that have taken a porch and converted it to a great 4-seasons room only to find out it is unusable because the temperature is out of control and running ductwork is practically impossible.  The folks that had a general contractor build them a beatiful room with a couple of supplies stolen from the closest duct only to find it was only bearable to stay inside the room unless conditions were just right.  The folks that built a new sunroom and knew they needed some kind of HVAC solution but didn't want to settle for a PTAC or window unit for their needs.  For those folks, we offer and highly recommend a ductless minisplit system.  

A minisplit is a technology that is familiar to some and completely foreign to others.  At it's core, it is a split system like most central air systems found in homes, with an inside air handler/evaportaor unit and an outdoor condensor/compressor unit that are connected by refrigerant, power, and communications lines.  The key difference is that it doesn't use ductwork to distribute the air, but rather the wall mounted indoor unit handles moving the air in an attractive and discrete package.  While these units can also be used to heat and cool an entire home very effectively, they're almost tailor made for Sunrooms.  They are quiet, efficient, powerful, and did I mention quiet?  These units are completely independent from the central HVAC system and as such can either keep the room perfectly comfortable or be completely switched off if the room isn't being used.  They come in a range of options from cooling only non-inverter compressor units to hyper-heat High output heatpumps with an inverter compressor that is able to vary its output to match the exact need of the room while producing enough heat to keep a room comfortable until it's almost zero degrees outside.

So, back to the title and the whole reason for this post - if you have an area of your home that is not comfortable, you might as well not have it.  I can't say it any better than one of the customers that we installed a system for.  She said "We didn't even have this room until we had our mini-split installed".  So, if you've got a room that's plagued by comfort issues and you would like to reclaim that space, drop us a line and find out what options might work for you.